In T 487/13 the board held that, by deciding not to admit auxiliary requests 4 to 6 directly after late-filed document D10 was admitted into the proceedings, the opposition division did not respect the appellant's right to be heard, which was inextricably linked to the principle of fair and equal treatment of the parties. Since these new requests were filed in direct response to a change in the subject of the proceedings, they were submitted in due time and the opposition division had no discretion to disregard them.
Likewise, in T 754/16 the opposition division had not admitted auxiliary requests 8 and 9, filed during oral proceedings, on a prima facie basis (referring to Art. 114(2) and R. 116 EPC). The board noted that this presupposed, in the first place, that the requests were late (confirming T 273/04). This was however not the case since filing the auxiliary requests was a direct response to the opposition division's change of opinion in the oral proceedings. Under R. 116(2) EPC, requests filed after the final date set for making written submissions can only then not be admitted if the patent proprietor had been notified of the grounds prejudicing the maintenance of the patent, which was not the case here. See also T 586/16.
In T 966/17, however, the board explained that, in opposition proceedings, R. 79(1) EPC allowed the patent proprietor to amend the description, claims and drawings within a period set by the opposition division. Later amendments, by contrast, were admissible only at the opposition division's discretion, as was clear from R. 81(3) EPC for instance. The board then considered that the opposition division's expression of a different opinion at the oral proceedings from the one provisionally set out in the communication accompanying the summons was not enough by itself to deprive it of that discretion and oblige it to admit whatever requests were filed at the oral proceedings. It was permissible, the board held, for the decision on admitting new requests filed by the appellant in response to a new line of attack taken by the opponent on the basis of a newly filed document to take into consideration whether those requests were prima facie allowable or would anyway have to be refused owing to other objections already raised at a previous stage in the proceedings. See also T 908/19, in which the board considered that the auxiliary request had been filed in due time in accordance with R. 79(1) EPC and that therefore the question whether it was "clearly allowable" was not relevant.
Another approach was taken in R 6/19. In this decision the Enlarged Board pointed out that the right, found in the second sentence of Art. 123(1) EPC, to at least one opportunity to amend, does not extend to a patent proprietor in opposition proceedings. It concluded that the opposition division had the discretion, given in the first sentence of Art. 123(1) EPC, not to admit such requests.