In T 134/88 the opposition did not deal with all the features of the contested claim, but still satisfied the requirements of R. 55(c) EPC 1973 (R. 76(2)(c) EPC). The board summed up by saying that an opposition directed against alleged lack of inventive step in the case of a combination invention was generally inadmissible if it related only to the assessment of one individual feature. To be admissible, it would have to deal with the invention as a whole, or at least with its essential content, so that when the facts on which the opposition was based were indicated, circumstances became recognisable which enabled the patent proprietor and the assessing body to pass conclusive judgment on the asserted grounds for opposition without having to make enquiries of their own. Allegations which could not be subsumed under one of the opposition grounds have to be left out of consideration (see also e.g. T 1279/05, T 114/07, T 521/00, T 1074/05). A detailed and exhaustive discussion of matters which were implicit to such skilled persons was not needed to understand the opponent's case and, therefore, not an admissibility requirement. See also T 534/98, in which it was held that evidence of the common general knowledge was not required to substantiate an opposition. In accordance with the prevailing view in the case law, proof that something belonged to the common general knowledge was only necessary if this was called into question by another party or by the EPO.
In T 1014/09 the opposition was based on the inadmissibility of an amendment (replacement of "carrier housing" by "intermediate housing") "because it was not covered by the original disclosure". The board had to establish to what extent this general reference to the original disclosure could be regarded as a due indication of the facts, evidence and arguments within the meaning of R. 55(c) EPC 1973 (R. 76(2)(c) EPC), and to what extent the assessment of the amendment to the claims as "misleading" could be construed as an indication that the amendment had unlawfully changed or extended the technical information. The board concluded that the facts of the case at issue and the accompanying legal analysis set out in the notice of opposition had to be regarded as duly substantiating the ground for opposition under Art. 100(c) EPC.
In T 185/88 (OJ 1990, 451) the board ruled that grounds for opposition are deemed to be in due form if the only document cited in support of the sole assertion of lack of inventive step (here: German patent specification), while itself published after the date of filing or priority, nevertheless contained a reference to a document published before the date of filing or priority (here: German unexamined application or "Offenlegungsschrift").
In T 864/04 the board had to examine whether the express mention of document D1a in the notice of opposition in relation to D1 by the statement: "(divided out inter alia of US-PS No. 5,290,583)" was sufficiently precise to enable the patentee to find out the date of the publication of this document. In the Board's view, this was indeed the case because no undue burden was involved to discover D1a's publication date. The opposition was considered admissible.
In T 623/18 the board guarded against a too strict approach. The board emphasised the purpose of the statement under R. 76(1) EPC and R. 76(2)(c) EPC, as explained in G 9/91 and G 10/91 (OJ 1993, 408 and 420), namely to define the extent and scope of the opposition and the legal and factual framework, within which the substantive examination of the opposition is in principle conducted, as well as to give the patentee a fair chance to consider his position at an early stage of proceedings. The board saw no basis for making admissibility of the opposition dependent on the assessment of substantive questions, in particular on whether an objection merely related to a lack of clarity or could support the ground for opposition under Art. 100(b) EPC. It was also a matter of substantive examination to characterise the person skilled in the art, for whom, according to Art. 100(b) EPC, the description should be sufficiently clear and complete, and for whom obviousness over the prior art was to be assessed according to Art. 100(a) EPC in combination with Art. 56 EPC.