In accordance with the Enlarged Board of Appeal's decision in G 1/95 (OJ 1996, 615), alleged prior public use does not constitute a ground for opposition under Art. 100(a) EPC but is a fact cited to substantiate such a ground (T 190/05).
As stated above, a claim is deemed to be sufficiently substantiated if it can be understood by the EPO and the other parties without their having to investigate the matter themselves. Thus, the board will generally consider an allegation of public prior use only if it is sufficiently substantiated, i.e. where it can be readily seen how the public prior use took place (this was not the case in e.g. T 6/86, T 329/86 and T 78/90). If an opponent wishes to rely upon prior use as being part of the state of the art for the purpose of Art. 54(2) EPC and as part of the legal and factual framework within which the substantive examination of the opposition is to be conducted, the notice of opposition must indicate within the opposition period all the facts which make it possible to determine the date of prior use, what has been used, and the circumstances relating to the prior use.
An abstract indication of the subject-matter of the prior use is generally insufficient. Statements made within the period for opposition regarding the time, subject-matter and circumstances of the claimed public prior use must be intelligible enough from the viewpoint of the skilled person to enable their substantive legal merits to be reviewed. According to the established case law, the indication of facts, evidence and arguments need not be conclusive or correct. That is an issue of merit. A board, however, emphasized in T 1194/07 that the merits of a case can only be assessed in a meaningful manner if the case has been stated fully, by an adequate indication of the relevant facts, evidence and arguments. Key elements linking the cited prior art to the claim or relating to their validity as evidence, as well as crucial arguments informing the reader why the skilled person might have considered combining the features of such prior art with those of the accompanying evidence, should not be missing in the notice’s chain of logic leading from the prior art to the invention. The omission of key facts and elements in the notice’s reasoning may amount to little more than speculation or an outline of a possible case against the patent.
In cases of alleged public prior use, particular substantiation is required in the notice of opposition. However, a distinction must still be made between examining the admissibility of the opposition and its substantive merit. Decisions T 194/86, T 328/87 (OJ 1992, 701), T 93/89 (OJ 1992, 718), T 232/89, T 538/89, T 754/89, T 78/90, T 600/90, T 877/90, T 441/91, T 602/91, T 988/91, T 541/92 and T 927/98 held that to be able to determine whether an invention has been made available to the public by prior use, the following circumstances have to be clarified:
(i) when the act of prior use occurred
(ii) what was made available to the public through that use
(iii) the circumstances of the act of use, i.e. where, how and by whom the subject-matter was made public through that use
The information relating to the "when", the "what" and the "how" of the circumstances surrounding prior use is all that the patent proprietor and the opposition division need in order to understand the case of the opponent and for the opposition to be admissible. The rest, i.e. whether the alleged facts were or would be sufficiently proven through additional filings in the course of the opposition proceedings, is a question of allowability in terms of substantive law. Thus, establishing that the alleged prior use is indeed public has little bearing on the admissibility of the opposition, but could be significant for assessing the allowability of the opposition in terms of substantive law (see T 406/92, T 786/95, T 1022/99; cf. also T 533/94, T 534/94, T 1553/07, T 25/08, T 1856/11).
In T 538/89 the board stressed that the evidence offered in support of public prior use could be submitted after expiry of the period for opposition since R. 76(2)(c) EPC (former R. 55(c) EPC 1973) only required that it be indicated (see also T 752/95, T 249/98). For instance, in the event of a purported sale to a small, closed group of customers, the requirements of R. 76(2)(c) EPC (former R. 55(c) EPC 1973) are met only if the name and address of the sole buyer are indicated within the opposition period (T 241/99). Nomination of a witness for a subsequent examination of the witness was deemed to constitute indication of evidence (see also T 28/93 and T 988/93).
Although a general offer of a witness testimony could not compensate for an inadequate presentation of facts; for the opposition to be admissible it is only necessary to name the witnesses. The naming of a witness to be heard later is therefore to be regarded as a sufficient indication of evidence as long as it is clear for what assertions of facts the witness is being named. It is neither necessary to indicate a specific subject in connection with evidence nor to indicate what the witness could say about a given assertion (T 1553/07).
In T 511/02, the question was raised as to whether the appellant (opponent) had fulfilled its duty of substantiation pursuant to Art. 99(1) EPC and R. 76(2)(c) EPC. The citations in the case at issue did not indicate when and how the fitting and installation instructions relating to the patent had been made available to the public. Since this factor was crucial to the establishment of whether the citations formed part of the prior art and thus whether they could actually be cited against the patent, no adequate indication had been given of the relevant facts and evidence (see also T 1271/06).
For more details on the evaluation of evidence in the case of alleged public prior use, see Chapter III.G.4.3.2.