In the recent Board of Appeal decision T 1946/21, Board of Appeal 3.2.03 held that it is sufficient for a transfer of the priority right to be effected on the filing date of the subsequent application, provided that applicant/patentee can demonstrate that the transfer had been effected at the time at which the subsequent application was filed. The Board did not follow appellant’s argument that the transfer had to be effected at the latest on the day preceding the day on which the subsequent application was filed.
Beware that (i) the EPO Guidelines (section A.III.6 in GL version 2023) include language (“the transfer of the application including the priority right (or of the priority right as such) must have taken place before the filing date”) that suggests that stricter criteria may apply, and (ii) national case law of EPC member states (such as BPatG 11 W (pat) 14/09, point II.B.2 a cited in T 1946/21) may require the transfer to have taken place at the latest on the day preceding the filing date.
Thus, if time allows, it is prudent to mitigate potential issues relating to the validity of the priority claim in Europe by (a) effecting a transfer of the priority right to the applicant of the subsequent application at least on the day before the filing date, or (b) filing the subsequent application with the applicant of the priority application being named at least as a co-applicant in the subsequent application.
T 1946/21 also includes interesting passages relating to partial priority issues in light of G 1/15.