T 1946/21 - (I) Transfer of priority, partial priority, and no shield effect of priority

Key points

• In this decision issued on 21.07.2023, the Board clarifies whether an assignment of a priority right must be executed at the latest on the day before the filing date of the subsequent application or can be executed on the day the subsequent application is filed but before the filing.
• "It is disputed whether the right to priority was validly transferred to the respondent and whether, therefore, the respondent was entitled to claim priority from the CN'506 application"
• "At the oral proceedings, the opponents agreed that the last question was decisive for the case in hand; if it were decided that in order to validly claim priority, the assignment could have been made on the day on which the subsequent application is filed, all the other issues would no longer be relevant."
• "It is settled case law that for the requirement of Article 87(1) EPC it is insufficient if the transfer agreement was concluded after the subsequent application was filed. The succession in title has to have taken place by the time the subsequent application is filed (T 577/11, Reasons 6.5.2; see also T 1201/14, Reasons 3.1.1.3). "
• There is no prior case law of the Boards about a same-day assignment.
• "There is a simple reason why the assignment of the right to priority need not be effective before the filing date of the subsequent application in order to meet the requirement of "successor in title" under Article 87(1) EPC: that is not what the law says."
• Introducing the requirement "would lead to the situation where a successor in title who obtained the right to priority on a certain day by way of an assignment always has to wait for the next day to file the subsequent application in order to enjoy its right to priority. In other words, the successor in title entitled to the right to priority because it was transferred to it on a certain day could not benefit from this right on that day. The Board cannot see any convincing reasons why this should be the case."
• "The applicant who on that day becomes successor in title could not file the subsequent application and enjoy a right to priority - they would have to wait until the next day but would then miss the deadline and be unable to enjoy the right to priority. The Board sees no reason for such unequal treatment."
• "It is down to the patent proprietor relying on the right to priority to demonstrate that the assignment was effective before the subsequent application is filed. Thus, if only the date on which the subsequent application was filed can be determined but not the exact time in the course of a day, the application may have to be considered to be filed at any time on the day of filing. If the assignment of the right to priority was then effective on that same date, the patent proprietor will not be able to successfully demonstrate that the then applicant had been the "successor in title" at the moment of the filing, i.e. that the assignment had been effective before the subsequent application was filed. This is not a question of legal certainty or treating applicants unequally; it is a question of fact which has to be proven by the applicant of the subsequent application claiming the right to priority.
• Indeed, it is down to the applicant filing the subsequent application to decide whether it is worth taking the risk of having to prove not only the filing date of the application and the assignment date but also the exact time of day of both. This may also depend on the chosen means of filing (delivery, postal services, electronic means) - the exact time of filing may be easier to prove for some means of filing than for others. It may thus be very much advisable, in order to avoid any issues of proof in this respect, to complete the transfer on the day before the subsequent application is filed. However, this is a decision for the applicant to make."
• As a practical tip, the applicant can just include a copy of the assignment with the filing documents of the subsequent application.
• "Taking into account the evidence on file, the Board considers that the respondent has indeed demonstrated that the contracts regarding the transfer of the right to priority had been validly concluded when it filed the subsequent application on 5 September 2014. This was not contested by the appellant or the intervener (see point 2.2 above). In view of the above considerations, the Board thus concludes that the then applicant was indeed the "successor in title" who enjoyed the right to priority within the meaning of Article 87(1) EPC.'

Partial priority

• Now turning to truly EQE D stuff.
• The application claims the priority of 8 Chinese patent and utility model applications applications and one Dutch patent application. The applicant is a US legal entity, the inventors are Chinese. The CN utility model application was published in the priority year.
• "The appellant and the intervener argued that the disclosure of [Chinese utility model application] D29 could not provide a priority right for the general subject-matter of claim 1 as granted. Consequently, the content of D29 - corresponding to a particular embodiment of the general subject-matter claimed in the contested patent - anticipated the subject-matter of claim 1, which was therefore not novel. In particular, no partial priority of claim 1 could be acknowledged in the light of the decision of the Enlarged Board of Appeal in case G 2/98 since D29 did not concern an alternative among a limited number of alternative subjects with regard to claim 1 as granted. Rather, claim 1 encompassed an unlimited number of alternatives when compared with the disclosure of D29.| 
• "The Board finds, however, that the principles established in G 1/15 apply to the case in hand."
• "In this Board's opinion, the Enlarged Board has indeed used the term "or otherwise" in the conclusion of G 1/15 to include all kinds of generalisations and thus to not be limited to the use in the subsequent application of a generic expression or a broadening of a chemical formula, etc."
• The Board does not admit the inventive step attack starting from D29. "the line of attack starting from D29 as the closest prior art is not taken into consideration (Article 13(2) RPBA 2020)."
• Question for the readers: how can D29 be cited as the closest prior art, given that the partial priority is found to be valid?
•  Assume that D29 teaches "gold" and the claim specifies "metal", the priority is invalid for the embodiments other than gold. Because D29 was published in the priority year, it can be fully cited against the claim embodiments lacking priority. The EPO does not have the shield theory of priority (see my post of 01.09.2017). It does not matter that the priority of D29 is claimed.
• Generally, a prior disclosure of "gold" would make it obvious to use other metals. However, this is a matter of fact and can depend on the circumstances. In the case at hand, the attack was late filed under Art.13(2) and the Board could dismiss it as not prima facie relevant because "Document D29 only discloses laminated elements arranged vertically in an annular array (see claim 1, and also page 3, lines 27-29, and paragraphs [0011] and [0025] of D29.1). The skilled person could not infer from D29 that the laminated elements could be arranged in a different orientation or so as to form an array which is not annular. " ... "the modification of the annular arrangement disclosed in D29 is not a mere design choice but would require a pointer in order to be considered by the skilled person. The appellant and the intervener have failed to indicate where the skilled person would find this pointer or why it belongs to the common general knowledge."
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EPO 

The link to the decision is provided after the jump, as well as (an extract of) the text of the decision.

https://new.epo.org/en/boards-of-appeal/decisions/t211946eu1.html

2. Main request - Novelty with respect to D29, Article 54 EPC - Priority right of claim 1 - Article 87 EPC

2.1 Reasons not to remit

With the intervention, lack of novelty over D29 was raised for the first time in opposition-appeal proceedings. As per G 1/94, an intervention under Article 105 EPC during pending appeal proceedings may be based on any ground for opposition under Article 100 EPC. However, pursuant to the Enlarged Board's opinion in G 10/91 for the exceptional situation of the introduction of new grounds in ordinary appeal proceedings, if the intervener raises a fresh ground for opposition, the case should be remitted to the department of first instance for further prosecution, unless special reasons present themselves for doing otherwise, for example when the patentee itself does not wish the case to be remitted (see G 1/94, Reasons 13). This is precisely the case in the proceedings in hand. As confirmed during the oral proceedings, the respondent did not want the case to be remitted to the Opposition Division for examination of novelty; it requested the Board to deal with this issue immediately.

2.2 Transfer of the priority right - Decisive issue

It is disputed whether the right to priority was validly transferred to the respondent and whether, therefore, the respondent was entitled to claim priority from the CN'506 application (D29, granted as CN 203 583 938 U).

In their submissions, the parties addressed several issues in this respect:

- whether these proceedings had to be stayed because the question of whether the EPO had jurisdiction to decide on the issue of the assignment of the right to priority was pending before the Enlarged Board (G 1/22 and G 2/22)

- which law was applicable in order to decide whether the applicant of the application in suit was the successor in title of the applicant of the priority application

- whether the right to priority had been assigned by way of an implicit agreement

- whether the right to priority had been assigned by way of a written agreement

- at what point in time the assignment of the right to priority had been made effective, including the question of whether a "nunc pro tunc" assignment was acceptable under Article 87(1) EPC

- whether the assignment had to be effective before the filing of the subsequent application or before the filing date of the subsequent application

At the oral proceedings, the opponents agreed that the last question was decisive for the case in hand; if it were decided that in order to validly claim priority, the assignment could have been made on the day on which the subsequent application is filed, all the other issues would no longer be relevant.

2.3 Transfer of the priority right - Validity of the transfer

As regards the question of whether the applicant is the "successor in title" within the meaning of Article 87(1) EPC, the Board finds that it is sufficient for the applicant or patent proprietor to demonstrate that the assignment of the priority right was effective before the subsequent application was filed. The law does not set forth any other condition. In particular, the assignment need not be effective before the filing date of the subsequent application. This is the case for the person who is "successor in title" either of the patent application including the right to priority or of only the right to priority.

2.3.1 It is settled case law that for the requirement of Article 87(1) EPC it is insufficient if the transfer agreement was concluded after the subsequent application was filed. The succession in title has to have taken place by the time the subsequent application is filed (T 577/11, Reasons 6.5.2; see also T 1201/14, Reasons 3.1.1.3). However, the case law has not been settled on the question of whether the agreement must have been concluded (T 577/11, Reasons 6.5.4), and thus the assignment must have been effective, before the filing date of the subsequent application or whether it is sufficient for this to have been done on the same day but before the actual filing. The Board is not aware of any case before the boards of appeal where this question was decisive. Therefore, any reference in the case law to "before the filing" or "before the date of filing" is irrelevant. As an example, T 1201/14 - mentioned in this respect by the parties - refers to both "before the filing" (Reasons 3.1.1.3 and 3.2.1.1) and "before the filing date" (Reasons 3.1.3).

2.3.2 There is a simple reason why the assignment of the right to priority need not be effective before the filing date of the subsequent application in order to meet the requirement of "successor in title" under Article 87(1) EPC: that is not what the law says.

Under Article 87(1) EPC, the applicant of the subsequent application must be either the person who filed the application (priority application) or the successor in title. In other words, once the applicant of the subsequent application is the "successor in title", they can enjoy the right to priority; if this applicant is not the "successor in title" because, for example, the right to priority was not validly transferred, they cannot avail themselves of this right. No further limitation is set forth in the law.

Reference can also be made in this context to G 1/15, in which the Enlarged Board held that, as a matter of principle, where a right was established by an international treaty or convention or by national law, it cannot be restricted by imposing supplementary conditions in administrative rules or guidelines or even in case law (G 1/15, Reasons 4.2). The Enlarged Board made this finding in relation to the substantive condition of "the same invention" within the meaning of Article 87(1) EPC. However, in this Board's opinion, that finding includes further confirmation that the right to priority enjoyed by the "successor in title" and enshrined in Article 87(1) EPC and Article 4A(1) of the Paris Convention cannot be restricted by requiring something that is not mentioned in the law, i.e. that the assignment of the right to priority be effective before the filing date of the subsequent application.

2.3.3 There is no reason to read such a requirement into the law either.

Doing so would lead to the situation where a successor in title who obtained the right to priority on a certain day by way of an assignment always has to wait for the next day to file the subsequent application in order to enjoy its right to priority. In other words, the successor in title entitled to the right to priority because it was transferred to it on a certain day could not benefit from this right on that day. The Board cannot see any convincing reasons why this should be the case.

Moreover, in that situation, it seems that nobody would be able to enjoy the right to priority for a certain amount of time. If the transfer occurred at noon, for example, the transferor could not benefit from this right in the afternoon because they would not be entitled to do so, and the transferee would not be able to use this right until the next day. Therefore, from noon to midnight on that day, no one could validly make use of the right to priority. The assumption could be made that the transferor holding the right at 0:00 on that day remained entitled for the entire day, essentially relying on the argument that the EPC only recognises a "day" as the smallest time unit. However, this argument must fail for the reasons set out below under point 2.3.4.

Lastly, reading the requirement of "before the filing date" into the law would mean that even though the applicant of the subsequent application has already obtained the right to priority and is in fact already the successor in title, it cannot make use of the full 12-month period under Article 87(1) EPC. The person who duly filed the priority application may file the subsequent application while enjoying a right to priority on the last day of the period. The applicant who on that day becomes successor in title could not file the subsequent application and enjoy a right to priority - they would have to wait until the next day but would then miss the deadline and be unable to enjoy the right to priority. The Board sees no reason for such unequal treatment.

2.3.4 The further arguments presented by the appellant and the intervener are not convincing either.

They argued that in patent law, in particular under the EPC, the smallest time unit is a day, and therefore an assignment on the day of the filing was insufficient. This was also what the German Bundespatentgericht considered in its decision BPatG 11 W (pat) 14/09, point II.B.2 a), subpoint cc) of the reasons, with reference to provisions of the German Patent Act.

At least for the EPC, there is no general rule of the smallest time unit being a day. It is true that the smallest time unit is a day when it comes to calculating and computing time periods (see Rule 131(1) EPC). This is applicable for example when calculating the 12-month period laid down in Article 87(1) EPC. However, the Board sees no reason why this should be generally applicable to other situations, in particular for the determination of the requirement of "successor in title".

It was further argued that applying time units smaller than a day would inevitably result in applicants being treated unequally. This was because the exact time of filing during the day depended both on the means used for filing and on the way the patent office dealt with the different means of filing, meaning that the filing time could not always be determined with precision. The principles of legal certainty and equality of rights would be violated.

This argument is not convincing either. It is down to the patent proprietor relying on the right to priority to demonstrate that the assignment was effective before the subsequent application is filed. Thus, if only the date on which the subsequent application was filed can be determined but not the exact time in the course of a day, the application may have to be considered to be filed at any time on the day of filing. If the assignment of the right to priority was then effective on that same date, the patent proprietor will not be able to successfully demonstrate that the then applicant had been the "successor in title" at the moment of the filing, i.e. that the assignment had been effective before the subsequent application was filed. This is not a question of legal certainty or treating applicants unequally; it is a question of fact which has to be proven by the applicant of the subsequent application claiming the right to priority.

Indeed, it is down to the applicant filing the subsequent application to decide whether it is worth taking the risk of having to prove not only the filing date of the application and the assignment date but also the exact time of day of both. This may also depend on the chosen means of filing (delivery, postal services, electronic means) - the exact time of filing may be easier to prove for some means of filing than for others. It may thus be very much advisable, in order to avoid any issues of proof in this respect, to complete the transfer on the day before the subsequent application is filed. However, this is a decision for the applicant to make.

2.3.5 The appellant and the intervener also relied on the principle of legitimate expectation, in particular because the Guidelines for Examination in the EPO had consistently referred to the requirement of "before the filing date" (reference was made to section A-III, 6.1).

The Board does not contest that the Guidelines for Examination may be a source of legitimate expectation. However, what the law requires from applicants in order for them to enjoy a right of priority cannot be determined by what is stated in the Guidelines for Examination, either directly or indirectly by way of creating a legitimate expectation. As concluded above, the requirement of "before the filing date" is not provided for in the law. It is irrelevant that the Guidelines for Examination consider this a requirement for a valid transfer. Nor can this become relevant if the principle of legitimate expectation is relied upon. Otherwise, the Guidelines could determine the existence of a requirement which is contrary to the EPC: the boards of appeal - which are undoubtedly not bound by the Guidelines - would become indirectly bound by them by virtue of the principle of protection of legitimate expectations. This principle cannot have this far-reaching effect.

2.3.6 In sum, to meet the requirement of "successor in title" within the meaning of Article 87(1) EPC, it is sufficient for the assignment of the right to priority to be effective before the actual filing of the subsequent application.

As pointed out above, it is always down to the applicant or patent proprietor relying on the right to priority to demonstrate that the assignment was effective before the subsequent application was filed.

Taking into account the evidence on file, the Board considers that the respondent has indeed demonstrated that the contracts regarding the transfer of the right to priority had been validly concluded when it filed the subsequent application on 5 September 2014. This was not contested by the appellant or the intervener (see point 2.2 above). In view of the above considerations, the Board thus concludes that the then applicant was indeed the "successor in title" who enjoyed the right to priority within the meaning of Article 87(1) EPC.

2.3.7 The conclusion in the preceding point has the following consequences for the case in hand. At the oral proceedings before the Board, the appellant and the intervener no longer contested these issues.

(a) The choice of the law relevant to the assignment in the case in hand (namely the law of California and the US, or Chinese law) is not decisive. In all cases the assignment was effective on 5 September 2014 at the latest, but before the actual filing of the subsequent application.

(b) The issue of the nunc pro tunc assignment is not decisive either. Nevertheless, this Board agrees with decision T 1201/14 (Reasons 3.2.1.1) in that regard: even if a retroactive transfer were allowable under US law, it would not be acceptable under Article 87(1) EPC.

(c) Lastly, it is irrelevant for the case in hand whether or not the EPO has jurisdiction to determine whether a party validly claims to be a successor in title (see G 1/22 and G 2/22). A stay of proceedings in view of pending cases G 1/22 and G 2/22 was thus not indicated.

2.4 Priority for claim 1

2.4.1 Disclosure of D29

Among the multiple priorities claimed in the contested patent, only CN'506U (D29) and NL'918 disclose laminated elements arranged in an air chamber as defined in claim 1.

The filing date of D29 is 5 December 2013 and it was published on 7 May 2014. The filing date of NL'918 is 4 December 2014. Thus, in the event that D29 were actually novelty-destroying for claim 1, NL'918 could not help in this respect.

Document D29 only discloses laminated elements arranged vertically in an annular array (see claim 1, and also page 3, lines 27-29, and paragraphs [0011] and [0025] of D29.1). The skilled person could not infer from D29 that the laminated elements could be arranged in a different orientation or so as to form an array which is not annular. Therefore, claim 1 as granted can only benefit from the priority right for the subject-matter of this particular structure.

2.4.2 Partial priority - appellant's and intervener's arguments

The appellant and the intervener argued that the disclosure of D29 could not provide a priority right for the general subject-matter of claim 1 as granted. Consequently, the content of D29 - corresponding to a particular embodiment of the general subject-matter claimed in the contested patent - anticipated the subject-matter of claim 1, which was therefore not novel. In particular, no partial priority of claim 1 could be acknowledged in the light of the decision of the Enlarged Board of Appeal in case G 2/98 since D29 did not concern an alternative among a limited number of alternative subjects with regard to claim 1 as granted. Rather, claim 1 encompassed an unlimited number of alternatives when compared with the disclosure of D29. The "intermesh spacers" of D29 were vertically arranged, whereas claim 1 encompassed any other orientation, including unclear borderline cases. As a consequence, claim 1 as granted did not correspond to a "generic 'OR'-claim" within the meaning of G 1/15 and no partial priority could be acknowledged. The meaning of "generic 'OR'-claim" had been determined in G 2/98 and the term required alternatives to be clearly defined, otherwise it would not be possible to conceptually divide the subject-matter as required by G 1/15.

2.4.3 The Board finds, however, that the principles established in G 1/15 apply to the case in hand.

The Enlarged Board in G 1/15 found as follows:

"Under the EPC, entitlement to partial priority may not be refused for a claim encompassing alternative subject-matter by virtue of one or more generic expressions or otherwise (generic "OR"-claim) provided that said alternative subject-matter has been disclosed for the first time, directly, or at least implicitly, unambiguously and in an enabling manner in the priority document" (see order; emphasis added).

A "generic 'OR'-claim" is not limited to the situation in which the claim encompasses alternative subject-matter by virtue of a generic expression. Rather, other situations also fall under this concept, as acknowledged by the words "or otherwise" in the order of G 1/15.

The Enlarged Board addressed various situations in G 1/15, including the broadening of a chemical formula, of a range of values and of chemical compositions, as well as other generalisations. This can be seen in particular in the summary of T 1496/11 in Reasons 2.2 (under the heading "Other generalisations"); that case related to a generalisation through the omission of more specific indications, with the claim in question thus encompassing embodiments including features produced by means other than those omitted. It is also evident from the summary in Reasons 2.3, in which the Enlarged Board explained that - in addition to the above-mentioned examples of broadening - the presence of other generalisations compared with the invention disclosed in an enabling manner in the priority document had led to partial priority being denied because the claim of the subsequent application did not spell out a "limited number of clearly defined alternatives", even though the requirement of identity of invention had been met for at least some alternative embodiments disclosed in the priority document and encompassed by the generic "OR"-claim.

In this Board's opinion, the Enlarged Board has indeed used the term "or otherwise" in the conclusion of G 1/15 to include all kinds of generalisations and thus to not be limited to the use in the subsequent application of a generic expression or a broadening of a chemical formula, etc.

The appellant's and the intervener's argument that the claim encompassed an unlimited number of alternatives, meaning that partial priority could not be acknowledged, is not convincing. The fact that very many alternatives could be identified is not a reason for denying that there was a generic "OR"-claim or, more generally, for not applying the findings in G 1/15. The appellant's and the intervener's argument essentially relies on the requirement of a "limited number of clearly defined alternatives", which is taken from G 2/98, Reasons 6.7. However, this (additional) requirement for acknowledging partial priority was explicitly rejected by the Enlarged Board in G 1/15; see Reasons 5.3, 6.7 and the last sentence of the order. Any such requirement would be nothing more than a supplementary condition restricting the right to priority established by the EPC, which is contrary to G 1/15, Reasons 4.2, last paragraph.

The Enlarged Board acknowledged in G 1/15, Reasons 6.6 that the task of determining the relevant disclosure of the priority document taken as a whole, and determining whether that subject-matter is encompassed by the claim in the subsequent application (see G 1/15, Reasons 6.4), could generally be a demanding intellectual exercise but was common practice at the EPO and among practitioners of the European patent system.

This exercise is, moreover, not difficult in the case in hand, in which the priority document itself is the allegedly novelty-destroying disclosure. In this situation, the (partial) priority of the claim based on this priority document is valid for every potentially novelty-destroying element disclosed in this very same priority document. This is the case no matter where the conceptual division in the claim is actually to be made. As explained in G 1/15, Reasons 6.4, the first part of the conceptual division corresponds to the invention disclosed directly and unambiguously in the priority document. The second part is what the Enlarged Board called "the remaining part" of the generic "OR"-claim. The remaining part is anything that is not the directly and unambiguously disclosed first part, regardless of precisely what alternatives the remaining part consists of (including what the appellant and intervener called "borderline cases") and regardless of whether this part has an unlimited number of alternatives.

On condition that G 1/15 indeed applied to the case in hand (as decided by the Board for the reasons set out above), the appellant and the intervener did not contest this analysis any further.

2.4.4 Thus, the subject-matter of claim 1 (in its entirety) is novel over D29 (Article 54(2) EPC) since the claim enjoys partial priority from that document for all the encompassed subject-matter disclosed in it.

3. Main request - Inventive step, Article 56 EPC

3.1 D29 as the closest prior art - Admittance, Articles 13(2) and 14 RPBA 2020

3.1.1 The line of attack starting from D29 (the priority document discussed above as allegedly being novelty-destroying) as the closest prior art in combination with the skilled person's common general knowledge cannot be accepted as it was late-filed (Article 13(2) RPBA 2020).

3.1.2 The appellant and the intervener had become aware of the respondent's arguments concerning the disclosure of D29 after receiving the respondent's reply to the notice of intervention. This reply made it clear what the distinguishing features of claim 1 over D29 were considered to be, namely "the annular features" (see reply to the notice of intervention, point 3.2.2).

3.1.3 Contrary to the appellant's assertion, its letter dated 14 October 2022 did not include this line of attack, let alone in a substantiated manner. Even though the heading of point 7. read "Lack of novelty / inventive step over D29", this does not count as having validly raised the particular line of attack, for want of proper substantiation.

Point 7.1 of that letter does focus on the differences between the subject-matter of claim 1 as granted and the disclosure of D29. However, point 7.2 does not explain the logical chain which would lead the skilled person towards implementing the distinguishing features in D29, especially since the appellant itself stated in the same letter that the distinguishing features "involve further technical considerations" (see page 11, third and fourth paragraphs of point iv.). Points 7.2 and 7.3 fail to provide an explanation as to how the skilled person would apply - in an obvious manner - the claimed solution in the pool of D29 in order to address the objective technical problem related to the technical effect provided by the distinguishing features, let alone in consideration of their common general knowledge.

The appellant merely quoted (fourth paragraph on page 12) a statement made by the respondent in its reply to the notice of intervention that bears no relation to the skilled person's common general knowledge related to the shape of a pool; it merely states what the skilled person would have regarded as being directly and unambiguously disclosed in D29 in connection with the shape of the pool disclosed in that document. The quotation from the respondent's reply in fact relates to the opposite attack to the one being raised, i.e. that the skilled person starting from a non-annular pool would have thought of implementing the disclosure of D29 in this closest prior art: "The skilled person would have readily understood that the invention [i.e. D29] is applicable to pools with non-annular trough structures ...". This is the opposite of the current line of attack starting from the teaching of D29 in combination with the common general knowledge. Said difference is not a "purely formalistic" issue, as argued by the appellant during the oral proceedings, since the choice of the closest prior art fundamentally alters the logic chain which the skilled person must follow in view of the different distinguishing features, technical effects and objective technical problems resulting from each scenario.

Lastly, point 7.3 of the same letter merely states that the subject-matter of claim 1 is obvious "over D29 in view of the proprietor's own admission".

In view of the above, no substantiated line of attack starting from the teaching of D29 in combination with the skilled person's common general knowledge was raised in the letter dated 14 October 2022.

3.1.4 Consequently, the first time that the line of attack in question was presented in a substantiated manner was with the appellant's and the intervener's letter dated 30 March 2023, i.e. after notification of the summons to oral proceedings.

The legal basis for assessing the admittance of such an amendment to the appellant's and the intervener's case is Article 13(2) RPBA 2020.

3.1.5 The intervener cannot rely on any special status in the case in hand which would allow it to amend its case without the limitations defined in this legal provision.

Article 14 RPBA 2020 reads: "Where, during a pending appeal, notice of intervention is filed, Articles 12 and 13 shall apply in so far as justified by the circumstances of the case." (emphasis added)

In this case, the notice of intervention was filed during the first stages of the appeal proceedings, namely six months after the notice of appeal had been filed. At that point in time, it was the intervener's right to file any ground for opposition and line of attack it wished to without being hindered by the provisions of Articles 12(4) to (6) RPBA 2020 since the intervener has the same rights and obligations as the other opponents irrespective of whether the intervention occurred during the proceedings before the opposition division or at the appeal stage (see Case Law of the Boards of Appeal, 10th edition, III.P.2 and III.P.3.1).

The intervener also reacted to the respondent's reply to the notice of intervention by means of a letter dated 4 November 2022. In this letter, it did not present a line of attack against the main request starting from D29, even though the heading of point 4. read "Invalid priority claim and lack of novelty / inventive step over D29".

Under these circumstances, the Board sees no reason why Article 13(2) RPBA 2020 should not apply to an amendment to the intervener's case, since the delay in filing the new line of attack cannot be attributed to its status as an intervener but rather to its choice of strategy once it had joined the appeal proceedings.

3.1.6 No exceptional circumstances can be discerned in relation to the late filing of the new line of attack.

The appellant and the intervener were aware of the issues related to the partial priority of claim 1 and the subsequent distinguishing features of the subject-matter of this claim over D29 once they had received the respondent's reply (dated 28 September 2022) to the notice of intervention. However, neither the appellant's letter dated 14 October 2022 (see point 3.1.3 above) nor the intervener's letter dated 4 November 2022 (see preceding point) presented the new line of attack in a substantiated manner.

3.1.7 Furthermore, the line of attack is not prima facie relevant.

As acknowledged by the appellant in the letter dated 14 October 2022, the distinguishing "annular features" are linked to technical considerations in terms of the distribution of forces in the resulting structure (see page 11 of the letter, third paragraph of point iv.). Thus, the modification of the annular arrangement disclosed in D29 is not a mere design choice but would require a pointer in order to be considered by the skilled person. The appellant and the intervener have failed to indicate where the skilled person would find this pointer or why it belongs to the common general knowledge.

3.1.8 The appellant and the intervener argued that the respondent did not invoke the alleged late filing of the line of attack starting from D29 until the oral proceedings.

However, this is irrelevant when discussing the admittance of a late-filed line of attack. Article 13(2) RPBA 2020 establishes restrictions related to amendments to a party's case, and these are not dependent on whether other parties take them as a basis for a request not to admit a late-filed amendment into the proceedings.

Moreover, the respondent could not object to the late filing of the new line of attack until it had been presented in a substantiated manner. This happened with the letter dated 30 March 2023 (see point 3.1.4 above), i.e. barely one month before the oral proceedings. Even under this tight schedule, the respondent requested in its letter dated 25 April 2023 that the amendments presented with the other parties' last letter - including the new line of attack starting from D29 - not be admitted into the appeal proceedings (see page 1 of the respondent's letter, first complete paragraph, and also points 3.a. and 3.b.).

3.1.9 Consequently, the line of attack starting from D29 as the closest prior art is not taken into consideration (Article 13(2) RPBA 2020).