In T 674/91 the board stated that all the assertions (affidavits or declarations) made by different witnesses of the alleged prior use and which were in agreement with one another already provided sufficient evidence of the commercial nature of the tests mentioned. An obligation of confidentiality could not have existed, since the access to the new tool was not restricted to a particular group of persons. The board concluded that the prior use was prior art within the meaning of Art. 54(2) EPC 1973.

The board in T 1682/09 held that evidence from an independent source corroborating an alleged prior use would have constituted strong evidence in support of the allegation, but the mere absence of such independent evidence was not a sufficient reason to dismiss it.

In T 1452/16 the alleged prior use concerned a product which was commercially available as agreed by all parties. It was thus possible for the patent proprietor to simply obtain samples and test them. Even if the present case did fall into the category of "balance of probabilities", the board did not merely form its opinion on the basis of whether the alleged facts were just slightly more likely to have occurred than not, but on the basis of whether it was convinced that they had occurred.

In T 225/03 the opposition division had not taken evidence by hearing the witness before revoking the patent because it had considered the allegation of public prior use to be adequately proven by the documentary evidence. The board found that level of proof to be insufficient, and held that the respondent's (opponent's) request – that the documentary evidence be complemented by hearing the witness – had to be granted, as only the witness could confirm the links between the individual pieces of evidence and the circumstances of use as explained in his statutory declaration. It therefore sent the case back to the department of first instance for further prosecution.

In T 441/04 the board agreed with the respondent (patent proprietor) that evidence in document form was normally preferable to witness testimony about long-ago events. But that did not mean that in the case in point such testimony was necessarily excluded per se or less convincing than documentary evidence. Applying the (high) standard of proof beyond doubt, the board considered that it had taken due account of the fact that the alleged public prior use – proven by witness testimony – was attributable to the appellant. The evidence submitted (mainly witness testimony) had measured up to that standard, and therefore no new or additional proof (such as drawings) was needed.

In T 1914/08 the board – like the opposition division at first instance – regarded two witnesses' testimonies as the decisive evidence proving without any gaps the alleged prior public use. Each testimony, considered in isolation, gave a consistent and full picture of the process in question. Accordingly, it endorsed the opposition division's evaluation of the evidence, the standard of proof applied by it ("beyond all reasonable doubt") and the result of its analysis. It held, moreover, that the patent proprietor's (appellant's) request for additional evidence had to be refused. Since the opposition division had, in the course of its unfettered consideration of the evidence, concluded that the alleged prior public use had, essentially, been established by the two witnesses' testimonies and since the appellant had been unable to cast doubt on the probative value of those testimonies, there was no need for the opponent (respondent) to adduce further evidence in either the opposition or the appeal proceedings.

In T 833/99 the opponent (appellant) had raised a novelty objection, claiming that prior use had occurred following public disclosure of an identical process: grooved-rail frogs for tramlines had been sold and installed in various German towns over a specified period. The opposition division had found this disclosure to be insufficiently proven, and had duly dismissed the objection. In support of its contention that the manufacturing process lacked novelty, the opponent relied on two photos (showing the grooved-rail frogs) measuring 6 cm by 6 cm and appearing inside a prospectus. The photos were not clear enough to say that the edges could not have been the result of flame-cutting. Lastly, during invitations to tender, the municipal employees had been required to observe confidentiality. The appellant said they might have breached that confidentiality, e.g. by informing repair workers of certain steps in the process, but did not back this up with firm facts such as dates, circumstances, etc., or with other evidence. Mere suppositions could not be entertained; they were not proof, and the onus was on the appellant to show that its allegations were well founded (T 782/92; T 472/92, OJ 1998, 161). Lastly, the board observed that there was no law to the effect that the confidentiality governing tender procedures ends when they do.

Features of subject-matter that was visible only briefly can be considered to have been made publicly available only if it can be shown beyond doubt that they were clearly and directly apparent to the skilled person for that short time (T 1410/14: train – test drive).

In T 2565/11 the invention concerned a method of operating a ventilator and air conditioner for vehicles. It was not contested that the trains which were the subject of a prior use allegation were indeed delivered to DB Regio AG and operated in a public manner. However, it was disputed that information concerning the ventilation and air conditioning system of those trains was published in the sense of Art. 54 EPC by the delivery and operation of the trains and further that the structure and operation of the ventilation and air conditioning system had been adequately proved by the opponent. In its decision the opposition division held that the alleged public prior use had not been proven beyond reasonable doubt. The board, in the case at hand, overturned the evaluation of evidence made by the department of first instance because the opposition division erred as regards the underlying facts and failed to give an evaluation that was free of contradictions. The board gave its own evaluation of the evidence regarding the relevant facts. Even applying a high standard of proof ("beyond any reasonable doubt"), the board found that the basic facts presented by the witness could not be questioned.

Decisions applying the boards' case law on the strict standard of proof – initially established for public prior use – to other matters include T 1107/12, on the accessibility of documents, and T 1201/14, on proof of the transfer of priority right.

See also chapter V.A.4.13.6 b) "Consideration of late-filed evidence of public prior use".