An allegation of public prior use will generally only be considered 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 alleged public prior use must be intelligible enough from the viewpoint of the skilled person to enable their substantive legal merits to be reviewed.
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. It is settled case law (see e.g. 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) 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 its allowability 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 241/99, for instance, the board considered it insufficient for the purposes of R. 55(c) EPC 1973 (cf. R. 76(2)(c) EPC) that, in the event of a purported sale to a small, closed group of customers, these were identified only by a coded indication (list of numbers). This was different from the sale of mass-produced goods to anonymous buyers and resembled rather the case of a single sale, for which the requirements of R. 76(2)(c) EPC were met only if the name and address of the sole buyer were indicated within the opposition period.
In T 511/02, concerning the opponent's duty of substantiation, it had not been indicated when and how fitting and installation instructions cited against the patent had been made available to the public. Since this factor was crucial to the establishment of whether they 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).
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. 55(c) EPC 1973 (cf. R. 76(2)(c) EPC) only required that it be indicated (see also T 752/95, T 249/98).
According to the board, nomination of a witness for subsequent examination is deemed to constitute indication of evidence (see also T 28/93, T 988/93 and T 241/99). Although a general offer of a witness testimony cannot 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).
The evaluation of evidence in cases of alleged public prior use is dealt with in detail in Chapter III.G.4.3.2.
Under Art. 114 EPC the EPO has a limited obligation to undertake an examination of its own motion with regard to public prior use.
In T 129/88 (OJ 1993, 598) the board noted that although a board of appeal had an obligation under Art. 114(1) EPC to investigate matters of its own motion, that obligation did not extend as far as investigating an allegation of public prior use, where the party previously making that allegation had withdrawn from proceedings and it was difficult to establish all the relevant facts without that party's co-operation. The reason for this was that the obligation to investigate of its own motion imposed on the EPO by Art. 114(1) EPC was not unlimited in its scope, but was confined by considerations of reasonableness and expediency. Therefore, if the opponents withdrew the opposition, thereby indicating that they were no longer interested in the outcome of the opposition, then, although the EPO might have the power, depending on the state of residence of relevant witnesses, to compel them to give evidence, either before the EPO or before the court of a contracting state, in the interests of procedural economy it should not normally investigate the issue any further. It would be different if a relevant public prior use had already been substantiated by documents of undisputed authenticity, or if the material facts with respect to the alleged public prior use were undisputed (see T 830/90, OJ 1994, 713; T 887/90, T 634/91, T 252/93 and T 34/94).