In T 182/89 (OJ 1991, 391) the board observed that in order to establish insufficiency, a mere statement by an opponent that one example in a patent had been repeated once "exactly as described" without obtaining exactly the described results as set out and claimed in the patent was clearly inadequate. On the question of substantiation, the board took the view that, if a notice of opposition alleging insufficiency under Art. 100(b) EPC 1973 as the sole ground for opposition contained such a statement as the only indication of "facts, evidence and arguments" in support of this ground, then the notice of opposition should be regarded as inadmissible even if the alleged facts were subsequently proved.

In T 550/88 (OJ 1992, 117) the board of appeal considered whether national prior rights could as a matter of law constitute "facts or evidence" relevant to the ground of lack of novelty under Art. 54(1) and (3) EPC 1973. In the board's judgment, on the proper interpretation of Art. 54(3) EPC 1973, national prior rights were not comprised in the state of the art, and only prior European patent applications filed under the Convention could be considered as such under Art. 54(3) EPC 1973. The board decided that the opposition was inadmissible because the only facts and evidence indicated in the notice of opposition were references to national prior rights.

According to T 613/10, the admissibility of the opposition has to be decided in the light of the circumstances of the case, especially if the requirements of R. 76(2)(c) EPC are not clearly and unambiguously met. Those circumstances include not just the technical complexity of the subject-matter in the opposed patent and the citations but also the number of claims and the number of citations – even if in principle an opposition can contain any number of attacks or citations. The patent proprietor should not have to try and work out the opponent's case for himself, from inadequate information given in the notice of opposition. In the case before the board, notice of opposition had been filed within the opposition period on the official form and two additional sheets. These listed 26 items of evidence, which however were filed, together with a detailed statement, only after the period expired. The notice had indicated the grounds of lack of novelty and lack of inventive step but did not say which citations related to which. None of the cited passages or drawings had been compared with the features of any of the 26 claims; nor had any technical connection been established between the citations and the claims. The board concluded that the notice of opposition did not properly indicate the facts presented in support of either of the two grounds, so that the requirements of R. 76(2)(c) EPC were not fulfilled.