In T 736/95 (OJ 2001, 191) the ground referred to by the appellant under Art. 100(c) EPC had not been raised in the notice of opposition. The opposition division had decided not to admit the newly submitted ground, without giving the parties any indication that it considered it to be less pertinent. Having regard to G 10/91 (OJ 1993, 420) and G 1/95 (OJ 1996, 615), the board held that the department of first instance at least had to examine whether a fresh ground was relevant and could therefore prejudice maintenance of the patent. Since it did not do so, but based its refusal to admit the ground only on the fact that it had been raised late, the opposition division deprived the appellant of the opportunity to have the relevance of this ground, and thus its admissibility, examined on appeal.

According to the board in T 520/01, where a ground was substantiated within the opposition period and the party which had raised the ground neither appeared at the opposition oral proceedings nor withdrew the ground, the ground had to be dealt with by the opposition division and could be taken up by other appellants in subsequent appeal proceedings.

In T 433/93 the board held that, in all normal cases, if an opposition division decided to introduce a new ground for opposition into the proceedings in addition to the ground(s) for opposition raised and substantiated in the notice of opposition, this should be done in writing as early as possible in the proceedings. The written notification to the patent proprietor from the opposition division informing the proprietor that a new ground for opposition would be introduced into the proceedings should at the same time ensure that the proprietor was informed not only of the new ground for opposition (i.e. the new legal basis for the opposition), but also of the legal and factual reasons (i.e. its substantiation) that would in effect substantiate the new ground which would lead to a finding of invalidity and revocation, so that the proprietor was fully informed of the case which he had to meet, and had a proper opportunity to present comments in reply. If, in a very exceptional case, an opposition division decided for the first time during oral proceedings that a new ground for opposition should be introduced, it would in principle be appropriate, even during oral proceedings, for the opposition division to notify the proprietor in writing both of the introduction of the new ground and of the legal and factual reasons which substantiated such a new ground. In this way, possible misunderstandings would be avoided, and the notification would be part of the written file record of the case.