Although the standard of proof is the same for all objections covered by Art. 100 EPC (cf. T 270/90, OJ 1993, 725), the case law identifies two levels or standards of proof to be applied with regard to disputes around public prior use - either the "balance of probabilities" or "up to the hilt". The standard of balance of probabilities is applicable when both the patent proprietor and the opponent had access to the material of which public prior use is alleged (see e.g. T 363/96, T 12/00, T 1105/00, T 2043/07, T 1464/05, point 4.3 of the Reasons; T 202/13, point 15.6.2 of the Reasons; T 1170/13, point 2.3 of the Reasons). 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"). Subsequent case law also confirmed that, where public prior use is cited, the assessment of probability which normally underlies the boards' opinion must yield to a stricter criterion close to absolute conviction (T 97/94, OJ 1998, 467; see also T 848/94 and T 12/00; recent case T 2451/13 discussed this concept). 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 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 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.
In T 1210/05, the board concluded that the contested prior disclosure via the public display of a poster identical to document (1) at an Edinburgh congress had not been sufficiently established, i.e. beyond all reasonable doubt, based on the following considerations: the fact that the various means of evidence, namely the submitted documents, the affidavits of the witnesses as well as their oral testimony, did not contradict each other was not sufficient to meet the required standard of proof. Furthermore, the finding of the opposition division rested exclusively on the testimony of one of the witnesses. No independent evidence (in writing or by other persons) was available to support it. This did not mean that the written and oral testimony of the witness was per se insufficient. However, the board stated that there had to be good reasons for treating this evidence alone as having established the facts beyond any reasonable doubt.
T 1057/09 concerned a "diploma thesis" whose content was allegedly disclosed inter alia during an oral presentation before the priority date of the patent in suit (ephemeral - beyond any reasonable doubt).
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 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).