In T 19/97 the board emphasised that there was a clear distinction between the substantive transfer of opponent status as a business asset and its procedural validity in the case at issue. As a formal requirement, the procedural validity of a transfer of opponent status was dependent on the submission of a duly substantiated request within the proceedings. On grounds of procedural certainty, a change of party based on an assignment could not take place outside the proceedings without the formal cognisance of the board and also could not have retroactive effect, as otherwise procedural acts or decisions could be respectively performed or taken without the involvement of the new opponent as the only legitimate party.

In T 956/03 the board considered the question of the time limit for filing evidence of a transfer. According to the board, the case law showed a definite balance in favour of the view that a transfer could only be acknowledged from, at the earliest, the date when adequate evidence to prove the transfer had been filed. This was desirable in the interest of legal certainty and, within that principle, to ensure that the identity of an opposing party was known. If the transfer took place before the appeal period expired, then the entitlement of the transferee to replace the opponent had to be established by filing the necessary evidence before the appeal period expired.

In T 428/08 the appellant had argued that it ought to be admissible to submit evidence of legal succession after the appeal period had expired, as evidence of prior use could also be submitted after the opposition period had expired without being rejected as grounds for opposition. The board did not follow this argument and relied on case law which made the date when the transfer became valid explicitly dependent on the date when evidence of it was supplied, in keeping with the procedural certainty requirement for the identities of the parties to the proceedings to be clear at all times.

In T 184/11 the board could not share the appellant's view that, following T 956/03, any transfer occurring before the appeal period expired also had to be substantiated by the end of that period. In T 956/03 the board had had to rule on the admissibility of an appeal filed by a party which maintained that it was successor in title to one of the opponents in the first-instance proceedings but failed to provide evidence of that within the appeal period. It was in that light that the principle set out in T 956/03 – that if a transfer occurred before expiry of the appeal period, then the evidence showing that the transferee was entitled to take the opponent's place also had to be submitted by the end of that period – was to be understood. In the case at issue, however, a party that had been opponent in the first-instance proceedings had initially been respondent in the appeal proceedings, and only during the latter was transfer of party status requested. This request was granted during the oral proceedings before the board, once the requisite evidence of the transfer of opposition had been provided. See also T 1563/13.

In T 6/05 the board drew a distinction between those cases where the opponent status is transferred together with the assignment of business assets and the cases of universal succession via merger – like the case at issue. Whereas in the former cases, the party status might either remain with the original opponent or be transferred to the new one, the universal successor of a patent proprietor automatically acquired party status in proceedings pending before the EPO, since R. 20(3) EPC 1973 did not apply in the context of universal succession in law. The successor acquired party status from the date on which the merger became effective and not only once sufficient evidence to this effect had been produced. The principles for transferring a European patent were to be applied mutatis mutandis to the transfer of opponent status. In the case of the universal succession of the opponent, there could only be one (legal) person who had rights and obligations, with the consequence that there was necessarily and automatically a continuation of the existing legal status as opponent from the date of merger. It could thus be established unambiguously and without any legal uncertainty, at any point in time in the proceedings who in fact was the opponent having party status, regardless of the date when sufficient evidence to this effect was filed (see also T 425/05 and T 2382/10).