Even though different concepts as to the standard of proof have developed in the case law of the boards, they all have in common that a judgement is to be made on the basis of the application of the principle of free evaluation of evidence. In the case of published documents, the standard of proof for public availability is usually the less strict one of the "balance of probabilities" (T 1140/09, point 3.2 of the Reasons). But even though the present case (date of availability in a public library of journal supplement disclosing meeting abstracts for a future conference) fell under the "balance of probabilities" standard for burden of proof, the board did not form its opinion solely 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 indeed occurred (T 1050/12).

The board in T 1107/12 found there was no indication that the opposition division had applied the wrong standard of proof, even if it had not explicitly discussed whether the strict standard of "beyond reasonable doubt" or the usual "balance of probabilities" standard should be applied. The case law requiring absolute certainty or proof beyond all reasonable doubt, which the respondent had cited in support of its position, was concerned with alleged public prior use (see T 441/04, T 472/92 and T 2451/13) and had applied that standard because, in such cases, the supporting evidence was almost always in the opponent's possession. The case in hand, however, turned on whether a document originating from one of the opponents had been publicly available on a particular date. Its availability was supported by witness testimony, the probative value of which was to be evaluated freely. Ultimately, there was no need for the board to decide whether the stricter standard of proof had to be applied in such circumstances too, since the opposition division's evaluation of the testimony had left it in no doubt as to its reliability or the witness's credibility as a person. Its evaluation of the evidence was not otherwise vitiated by any error in law. It was based on the right criteria, could be followed in all respects and did not contain any logical mistakes. It was therefore not open to the board to overrule its findings and re-evaluate the evidence in its place. See also T 2466/13 below, in which it was likewise found that there was no need to decide on the applicable standard of proof.