If notice of appeal was filed before the revised EPC entered into force, the appeal's admissibility must be assessed under the provisions of the EPC 1973, in line with the principle (tempus regit actum) that entitlement to perform a procedural act is governed by the law in force when the act took place (T 1366/04).

In J 10/07 (OJ 2008, 567) the board had to decide whether the EPC 1973 or the EPC 2000 applied. The decision whether an appeal is admissible according to the relevant provisions, geared to the fulfilment of the requirements for admissibility within a certain legally defined period, depends entirely on the substantive and legal position at the time of expiry of the time limits. Since the belated fulfilment of admissibility requirements after the expiry of the time limit cannot be taken into account in the examination of admissibility, so too a change in the legal position occurring after the expiry of the time limit for fulfilling the admissibility requirements can have no impact, either to the appellant's advantage or to his detriment, on the assessment of admissibility. In T 2052/08, the board, citing the finding in J 10/07 that R. 103 EPC should not be applied to appeal cases concerning patent applications filed before the entry into force of the EPC 2000, found that, as J 10/07 concerned the reimbursement of the appeal fee in situations where a substantial procedural violation had occurred at first instance, its conclusions should not be taken as implying a statement on the applicability of R. 103 EPC.

In T 616/08, the board found that, to the extent that it was relevant whether an aligned or the original version of a rule applied, there was a gap in the law which needed to be closed by case law as long as the legislator was not active. Art. 107, 109 and 111 EPC were not mentioned in the decision of the Administrative Council of 28 June 2001 on the transitional provisions under Art. 7 of the Act revising the European Patent Convention of 29 November 2000 ("transitional provisions"), although Art. 106, 108 and 110 EPC were. The board took into account the purpose of the transitional provisions (namely, to avoid the use of different versions of the EPC over a prolonged period), and the fact that there was nothing to indicate any intention to use new and old versions of Articles covering appeal proceedings in parallel. It therefore decided to apply Art. 107, 109 and 111 EPC and the rules appertaining to them where Art. 106, 108 and 110 EPC were applicable. The board referred to J 10/07 (OJ 2008, 567), where the Legal Board had concluded that Art. 107 and 111 EPC 1973 should be applied to applications filed before the cut-off date, but considered that the continued application of all EPC 1973 articles which had not been addressed in the transitional provisions did not appear to be in line with the legislators' objectives that the revised provisions should quickly take effect in practice and that the use of different variations of the EPC over a prolonged period should be avoided.