In the context of amendments to parties' cases, several decisions refer to the principles developed by the Enlarged Board of Appeal in relation to the inter partes appeal procedure provided for in the EPC, according to which such an appeal primarily serves the parties' right to a review of the first-instance decision in proceedings of a judicial nature. In G 9/91 and G 10/91 (OJ 1993, 408, 420) in particular, it was held that the main purpose of the inter partes appeal procedure is to conduct a final review of the decision given at the previous instance and thereby provide the losing party with an opportunity to challenge the decision against it and obtain a judicial ruling on whether it is correct. The appeal proceedings are thus largely determined by the factual and legal scope of the preceding opposition proceedings.

The parties are subject to certain restrictions on their procedural conduct, given, in particular, the need in inter partes proceedings to act fairly towards the other party and, more generally, the requirements of due process. The parties to inter partes proceedings are subject to a particular duty to facilitate due and swift conduct of the proceedings, which includes submitting all relevant facts, evidence, arguments and requests as early and completely as possible (T 1685/07, T 2102/08, T 253/10, T 1364/12). Admitting subsequent amendments to a party's case must not adversely affect the counterparty's right to submit observations on them (Art. 13(2) RPBA 2007), for example because it cannot duly exercise that right in the time then left (T 253/10, T 1466/12).