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".
Source: http://www.epo.org/law-practice/legal-texts/html/caselaw/2019/e/clr_iii_g_4_3_2.htm
Date retrieved: 17 May 2021