The boards began early on in their case law to set strict standards for the admissibility of late-filed evidence of public prior use by the opponent. On the basis of Art. 114(2) EPC 1973, they refused to include late-filed evidence in the proceedings where, in the specific circumstances, there had been an abuse of procedure and a breach of the principle of good faith. In such cases they chose to refrain from examining the potential relevance of the submission (see T 17/91; T 534/89, OJ 1994, 464 and T 211/90). In T 985/91 the board took the view, with reference to T 17/91, that late-filed documents should only be admitted into the proceedings under certain circumstances if they related to alleged prior use.

In T 17/91 an allegation of prior use based on the opponents' own activities had been filed two years after the expiry of the opposition period, with no good reason for the delay. This, in the board's view, constituted an abuse of the proceedings and a breach of the principle of good faith. Irrespective of its potential relevance, the allegation was therefore to be disregarded under Art. 114(2) EPC 1973.

Taking a similar line, the board ruled in T 534/89 (OJ 1994, 464) that an objection based on prior use by the opponents themselves which was raised only after the expiry of the opposition period, although the factual circumstances were known to the opponents and there was nothing to prevent the objection being raised during that period, constituted an abuse of procedure.

Four weeks before the oral proceedings in T 211/90 the appellant alleged public prior use for the first time. However, the evidence was already familiar to the appellant before expiry of the opposition period. The board held that the fact that the appellant was unaware of the relevance of this evidence, even though familiar with it at the time of filing the opposition, did not justify its introducing the evidence into the proceedings for the first time at such a late stage – irrespective of the reasons why it did not become aware of the potential relevance of this material until then. The board therefore decided not to consider this material in the further proceedings, without examining its potential relevance.

In T 691/12 the board observed that a prior-use allegation first submitted in the appeal proceedings could not be admitted and considered as prior art unless it met at least the following three conditions: (a) it did not involve an evident abuse of procedure; (b) the prior use as alleged had prima facie to be so relevant that it cast doubt on the validity of the patent; and (c) the prior use had to be fully proven, requiring no further investigation to establish its nature or context. In the case in point these conditions were not met (see also T 1847/12, T 63/13).

In T 2393/13 the board decided to disregard an unsubstantiated allegation of prior use. Under Art. 12(4) RPBA 2007, facts and evidence not only had to be submitted at the appropriate time; they also had to meet the requirements in Art. 12(2) RPBA 2007, i.e. they had to be complete. In other words, all the facts useful to establish when the prior use happened, what was used and the circumstances of that use should have been submitted to the board because only if it had had a complete case that adequately set out the relevant facts, evidence and arguments could it have usefully examined the allegation of prior use and come to a decision.

In T 481/99 the board said that the principle that late-filed facts, evidence and related arguments should only exceptionally be admitted into the proceedings by the opposition division (see e.g. G 9/91, OJ 1993, 408 and T 1002/92, OJ 1995, 605) did not imply that a late-filed allegation of prior use, which would be relevant if proven, was to be automatically disregarded on the ground that the new facts first needed to be established by taking evidence. However, if the submissions and/or documents relating to the late allegation of prior use showed inconsistencies or even contradictions, the deciding body was entitled to disregard the alleged prior use pursuant to Art. 114(2) EPC 1973 without further enquiries.

In T 380/00 the appellant (opponent) relied for the first time in the statement of the grounds of appeal on the non-confidential disclosure of technical features of the invention by an engineer during a job interview. The board considered that the alleged public prior use by the engineer was too poorly substantiated to justify further investigation of the matter.

On the issue of documents relating to prior use submitted during appeal proceedings, the board in T 508/00 ruled that poor communications within a company or a group of subsidiary companies did not constitute adequate and acceptable grounds for allowing the late submission of evidence concerning alleged prior use (see also T 443/09).

In T 1914/08, justifying why these documents had not been submitted until more than two years later and only shortly before the date set for oral proceedings, the respondent stated that it had been experiencing financial difficulties in the interim period. The board exercised its discretion in this regard and considered that, given the documents had been referred to and therefore available to the respondent from early on, their late filing without a justification which was causally linked to the proceedings was not in keeping with a proper conduct of the procedure. The late-filed documents were thus not admitted into the proceedings.

In T 884/14 the board held that the opponent's allegation of public prior use in the form of a product from its own company that it had not manufactured for a long time could certainly not be admitted if it had failed to look for that product from the outset, even though it had known of its existence and should have looked for it in its files in good time. That it had mistakenly believed there was no evidence could not excuse its failure to do so.

In T 1835/11, in its statement of grounds the appellant submitted new prior art – an alleged public prior use – without explaining why it had not filed it earlier. As the claims had not been amended in substance and the alleged prior use concerned sales of the appellant's own products, the board took the view that the appellant should have been able to file this prior art during the opposition proceedings.

In T 450/13 the board stated that not substantiating a public prior use in opposition proceedings but attempting to substantiate it in the statement of grounds of appeal could lead to the inadmissibility of such a line of attack under Art. 12(4) RPBA 2007.

Likewise in T 444/09, T 12/11, T 1295/12 and T 2361/15 no account was taken of a public prior use alleged for the first time in appeal proceedings.