The boards of appeal have developed various criteria for determining when, in the exercise of their discretion, they should consider latefiled submissions. These criteria have been incorporated into the RPBA (see Art. 13 RPBA in particular).
According to the established case law of the boards of appeal, filing new facts, documents and evidence would be considered to be in due time, if the filing was occasioned by an argument or a point raised by another party or in the appealed decision and could not have been filed before under the circumstances of the case. However, in order not to deprive the other parties of their right to verify the new evidence or to prevent the board from ensuring that the proceedings are conducted expeditiously, such facts and evidence have to be submitted once they are available and once it has become clear that they were relevant (T 201/92, T 951/91, OJ 1995, 202; T 502/98, T 730/07, T 320/08, T 976/10). Late filing is justifiable if it is an appropriate and immediate reaction to developments in the previous proceedings (T 855/96). Late filing is also admissible in order to support the reasoning to date (T 561/89) and to prove claimed common general knowledge, if challenged (T 106/97, T 1076/00). The delay is of less importance if the party was reacting to a finding in the contested decision (T 101/87, T 1511/06).The appellant who had lost the opposition proceedings should be given the opportunity to fill the gaps in its arguments by presenting further evidence in the second instance (T 406/09).
In T 101/87 the board drew a distinction between (a) the case of an opponent attempting to find further prior art when the opposition division had decided that the original citations did not warrant revoking or restricting the patent, and (b) the case of an opponent making a further search in response to substantial amendments of a claim or to comments from the opposition division regarding a missing link in a chain of argument. In the latter case, new documents could be admitted into the proceedings, instead of being regarded as late-filed.
In T 259/94 the appellants submitted new evidence - including documents reflecting common general knowledge and reports of tests - two years after filing the appeal. The respondent did not object to their introduction into the appeal proceedings. The board held that in such circumstances the principle of "volenti non fit iniura" empowered it to admit the late-filed evidence.
In T 1045/08 the board stated that where a party files new requests in appeal proceedings the other party must have the possibility of responding to these including the filing of new prior art documents, particularly when some of the amendments to the claims of the requests are based on features taken from the description of the patent. In this situation the concept of "late filed" must be considered relatively since the documents could not have been filed earlier because the party could not know the content of the future requests of the other party.