Under Art. 13(1) RPBA 2007 any amendment to a party's submissions after it has filed its statement of grounds of appeal or reply may be admitted and considered at the board's discretion.

According to established case law, discretion has to be exercised equitably, i.e. all relevant factors which arise in the particular circumstances of the case have to be considered (see G 7/93, OJ 1994, 775; R 11/11, T 931/06, T 936/09, T 23/10). In exercising its discretion the board takes account of the circumstances of the specific case, in particular the interests of the parties and the procedural economy of the appeal proceedings, having in mind the purpose of these proceedings (T 123/08).

In T 336/13 the board noted that the issue of discretionary power pertains to the merits of the decision and is part of substantive law (see R 1/13). Only an arbitrary or manifestly unlawful exercise of discretion amounts to a fundamental violation of the right to be heard pursuant to Art. 113 EPC (see R 9/11, R 10/11).