In T 332/87 a dated internal paper, marked as being confidential and not signed, was – together with an undated leaflet – not considered sufficient evidence. In T 595/89 the board decided that the opponent's in-house documents relating to the installation of a device in an aeroplane and to the sale thereof were not sufficient to prove public prior use.
In T 204/88 a letter of tender was not sufficient to prove public prior use because it was not discernible when and to whom the device was to be delivered and because the device was described in terms too general for anyone to identify whether it corresponded to the invention. In T 725/89 too, a dated tender was not regarded as sufficient evidence, as it was not proven when the tender had actually been presented, and the date of the tender was only one week prior to the priority date. By contrast, the board took the view in T 482/89 (OJ 1992, 646) that an unsigned delivery note, together with other documents, could constitute sufficient evidence of delivery.
In T 505/15 the board stated that the appellant's (opponent's) argument was credible that the original printed document was no longer available about 14 years after its creation, given that there was no obligation to keep the original paper version for more than 10 years. However, the board did not regard the lack of a signature as casting doubt on the content of the document. Firstly, the allegation of a legal requirement for signing such documents had not been substantiated. Secondly, even if the printed document was originally signed, it was unlikely that the electronically stored version of the document would contain such a signature. See also T 2466/13, which deals with both a failure to provide the originals of contracts assigning the right of priority and a mere allegation that a signature might have been forged.
In T 48/96 the board decided not to accept copies of pages from a catalogue bearing a date as sufficient proof of availability to the public. In order to prove the allegation that a particular apparatus described in a catalogue had been available to the public before the priority date, it was not sufficient to show that the catalogue had been published on time, because a mere indication in a catalogue did not constitute absolute proof that the described product had in fact been available to anybody; for example, there could have been a delay (see in this chapter III.G.4.3.4 a) for examples of cases concerning catalogues and commercial brochures, including T 1710/12, in which the board addressed the implications for the standard of proof where such a catalogue has not been produced in support of alleged prior use).
In T 905/94 the patent proprietor had exhibited a blind at an exhibition. After having considered the evidence regarding the exhibition the board looked at the question of whether use of the same trade name for different models could constitute evidence of the fact that the patent proprietor had marketed or described the blinds according to the patent at issue before the date of priority. In the board's opinion, such use could not constitute sufficient evidence since it was common practice in industry for the same name to be used and retained for a product, the technical characteristics of which changed over time as improvements were made. See also T 2020/13 on a change of trade name for prior-art products defined by that trade name.
In T 2357/12, concerning the transfer of opponent status and the concept of "universal succession", the board commented on the evaluation of evidence. The proprietor questioned the probative force of private documents, as submitted in this case, rather than public registration documents, as evidence of the transfer of opponent status in inter partes proceedings. The board stated that whereas public registers often enjoyed public trust regarding the facts registered and other public documents might be more conclusive on formal questions, the identity of the issuer and the date and place of creation of a private document could be more easily contested. However, neither kind of document provided irrefutable evidence of the correctness of a document's content. Citing examples of the different types of documents accepted in individual cases, the board pointed out that the boards had always accepted public and/or private documents as evidence of the transfer of rights, whether by way of universal succession or a single transfer of assets. The level of proof required was credibility of the facts for which evidence was given, in the light of all circumstances.
The opponent having died, in T 74/00 in the board's view, the best evidence which could be provided was evidence of the relevant law of succession (here, Japanese law) by way of legal opinion from a Japanese attorney-at-law; the mere filing of copies of a party's correspondence with his instructing Japanese attorneys could not serve as substitute. In T 205/14 (and T 517/14) Israeli law (applicable) was proved to the satisfaction of the board by an expert opinion provided by the party (right of priority – assignment). In T 1201/14, which also concerned transfer of priority, legal opinions were provided but did not satisfy the board on their merits.