4.5.2 Review of discretionary decisions by the boards
The discretionary power conferred by Art. 114 EPC necessarily implies that the EPO department of first instance must have a certain degree of freedom in exercising its power. A board of appeal should only overrule the way in which a department of first instance has exercised its discretion when deciding on a particular case if it concludes that it has done so according to the wrong principles, or without taking into account the right principles, or in an unreasonable way, and has thus exceeded the proper limits of its discretion (T 640/91, OJ 1994, 918; G 7/93, OJ 1994, 775; see also chapter V.A.3.4). This rule also applies with respect to opposition division decisions on the admission (T 1209/05, T 1652/08, T 1852/11, T 2513/11) or non-admission (T 1485/08, T 1652/08, T 1253/09, T 1568/12, T 1883/12, T 1271/13, T 1690/15, T 1711/16) of late-filed submissions. It is not the function of a board of appeal to review all the facts and circumstances of the case as if it were in the place of the department of first instance in order to decide whether or not it would have exercised such discretion in the same way (T 75/11, T 2685/19, T 1522/21; see however T 544/12, where the opposition division did not give sufficient reasons for its decision). In particular, the board should not interfere in such a discretionary decision simply because, under the same circumstances, the board itself would have decided differently (T 960/15).
This discretionary power has to be exercised reasonably after hearing the parties, including in oral proceedings if requested (T 281/00).
In T 435/20 the board found that the opposition division had decided according to the wrong principles and had disregarded the principles of procedural fairness and of equal treatment of the parties. Firstly, the board found inter alia that the mere fact that the opposition division's preliminary opinion was positive for one party could not in itself justify not admitting any further documents by this party which were filed by the final date set by the opposition division for making written submissions under R. 116(1) EPC. Secondly, as pointed out by the board, arguments submitted by a party's professional representative do not qualify as means of giving evidence under Art. 117(1) EPC and may therefore have a different weight depending on whether or not they are supported by further evidence. Accordingly, the opposition division was mistaken in holding that the declaration D81 with supporting documents on the one hand, and the representative's arguments on the other were equivalent and that this could justify non-admittance of documents D81 to D90. Further, D81 to D90 had been filed as direct and immediate response to new evidence submitted by the appellant on the last day for making written submissions under R. 116 EPC. In admitting this late-filed evidence into the proceedings but not admitting D81 to D90 filed by the respondents in direct response, the opposition division had not respected the principles of procedural fairness and of equal treatment of parties.
In T 879/21 the board considered that the opposition division had exercised its discretion using the wrong criteria and in an unreasonable manner when deciding not to admit the late-filed documents. The opposition division's finding that D15 to D17 were not prima facie relevant because the allegations that the claimed composites and foams could not be obtained and the objections of lack of disclosure, novelty and inventive step "were already brought forward in the notice of opposition" was unreasonable. With this reasoning, the opposition division had de-facto not assessed the prima facie relevance of these documents. The board found that if this approach were to be implemented, a party would lose the right to have any new evidence supporting an attack raised in the notice of opposition considered, irrespective of its prima facie relevance for the outcome of the proceedings.
See also in particular chapter V.A.3.4.1 "Principles applying to the review of first-instance discretionary decisions".