c) Justified response to new line of arguments in the board's preliminary opinion 

While it is incompatible with the convergent approach for a party to wait for the board's communication under Art. 15(1) RPBA instead of responding directly to the other parties' submissions (see chapter V.A.4.5.5a) above), a new line of arguments in that communication may well give rise to exceptional circumstances or at least be taken into account in assessing whether such circumstances exist.

In T 1309/16 the board admitted new citations (D23-D25) forming common general knowledge that had been filed in response to a new line of argument in its preliminary opinion.

In T 1038/18 the appellant (opponent), in reply to the preliminary opinion expressed by the board in its communication under Art. 15(1) RPBA, submitted for the first time during the appeal proceedings arguments of lack of inventive step over document D1 in respect of a claimed feature that did not correspond to the features identified by the opposition division as new but had subsequently been identified in the board's preliminary opinion as the sole distinguishing feature over document D1. The board did not agree with the respondent (patent proprietor), who objected that the appellant's arguments could have been submitted with the statement of grounds of appeal as precautionary measure and therefore should not be admitted. It instead acknowledged cogent reasons justifying exceptional circumstances and, in the exercise of its discretion under Art. 13(2) RPBA, admitted the appellant's arguments into the proceedings.

In T 1287/21 the validity of Annexes A to C, which served to prove the identity of a product used in the examples of the patent, was for the first time questioned in the proceedings by the board in its preliminary opinion. The appellant had not previously contested this evidence. In the board’s view the submission of Annexes E and F in response to the new arguments set out in the preliminary opinion was therefore justified by exceptional circumstances. See also T 1756/21 (expert statement in reaction to a new argument of the board).