By contrast, in cases where all evidence in support of an alleged public prior use lies within the power and knowledge of the opponent, while the patentee has barely any or no access to it at all, it is incumbent upon the opponent to prove the alleged prior use up to the hilt (T 472/92, OJ 1998, 161; cf. T 782/92 referring to proof "beyond any reasonable doubt"). The boards decided that the evidence lied within the sphere of the opponent: T 2451/13 and T 703/12 (prior use originating from a subsidiary of the opponent); T 202/13 (the opponent was the successor of the company directly involved in the alleged public prior disclosure); T 2338/13 (opponent bore consequences of lack of information on relationship between him, the witness whose testimony he was relying on and the person who had contacted the witness); T 703/12 (product presented at the Ambiente trade fair in Frankfurt); T 274/12 (subsidiary – talks between firms); T 544/14 (subsidiary); T 1469/08 (evidence presented involved opponent's company's sale); T 441/04 (witness testimony measured according to the high standard of proof beyond reasonable doubt); T 1682/09 ((the opponent's) packing system delivered to and mounted at a client's premises); T 1914/08, T 738/04, T 1776/14 (the two parties did not have equal access to evidence).

Decision T 918/11 (point 3.3 of the Reasons) summarised the case law on standards of proof and the conclusion drawn in T 750/94 (OJ 1998, 32), with the board also emphasising the need to take into consideration that the application of the strict standard of proof referred to in the impugned decision was not justified in view of the fact that the actual production and the selling of the containers was clearly outside the sphere of the opponent. The board was also of the opinion that the application of the standard of proof "beyond reasonable doubt" did not justify disregarding the witness testimony (regarding facts which had occurred a long time ago). The more recent decision T 2451/13 summarised the principles governing the standard of proof in case of public prior use and specified the meaning of the standard of "up to the hilt" (see Catchword) used in T 472/92, which is to prove beyond reasonable doubt. All the evidence about the publication date of a brochure was essentially in the hands of the opponent (brochure originated from a subsidiary of the opponent, on this latter point see also T 738/04).

If any reasonable doubt exists as to what might or might not be the result of carrying out the literal disclosure and instructions of a prior art document, in other words if there remains a "grey area", then the case of anticipation based on such a document has to fail (T 793/93; see also T 464/94 and T 95/07).

In T 2010/08, the board pointed out that the requirement to prove prior use beyond reasonable doubt could not be circumvented by overstretching the principle of ex officio investigation and so shifting the burden of proof from the opponent to the opposition division or the board of appeal.

The board in T 703/12 stated that all the evidence in support of the alleged public prior use (of a water filter jug, presented at the Ambiente trade fair in Frankfurt) lay within the power and knowledge of the appellant (opponent). The respondent (patent proprietor) disputed that the "what" was disclosed and that the "circumstances" of the prior use were proven beyond any reasonable doubt. The board was not convinced that either what was disclosed or the circumstances of the alleged disclosure had been proven to the required degree of certainty, namely beyond any reasonable doubt.

T 274/12 dealt with an alleged prior use (talks between firms), all the evidence being in the hands of the opponent. In this case the board had to also decide whether there was an implicit obligation to maintain secrecy.

In T 202/13 several public prior disclosures were alleged by the respondents (opponents). The board agreed with the appellant that the standard "up to the hilt", or "beyond reasonable doubt", was appropriate in the present case. One of the joint respondents 2 was the successor of the company directly involved in the alleged public prior disclosure. Respondent 2, as successor, had full knowledge of the actions alleged to constitute the public prior disclosure and full access to the sources of evidence.

In T 1469/08 the appellant (opponent) alleged a public prior use in the form of the sale of composite "PARP PU" prostheses before the patent's priority date. Although the public prior use stemmed from the opponent itself, it had provided only sales records to substantiate the prostheses' availability. In such circumstances, there were serious doubts that documents actually existed establishing the prostheses' availability to the public before the priority date. See also T 71/09, setting out the case law and citing T 750/94 and T 97/94. The respondent (opponent) alleged public prior use prejudicial to the novelty and inventive step of the subject-matter claimed. Here too, the prior use was its own: the evidence presented involved its company's sale of a certain product. The board held that the evidence submitted failed to establish the product's composition beyond any reasonable doubt.

In T 1776/14 the opponent stated that disclosure had been in its interest and implied that it was very likely the prior use had been public; in view of the circumstances, however, the board rejected its position and concluded that the balance of probabilities was not applicable because the two parties had not had equal access to the evidence.