The transfer must have occurred before the filing date of the subsequent application. According to T 1201/14, it was clear from the wording of Art. 87(1) EPC 1973 alone that the succession in title must have already taken place when the subsequent application was filed. The board in T 577/11 already confirmed that a succession in title that occurred after the filing date of the subsequent application was not sufficient to comply with the requirements of Art. 87(1) EPC 1973. This finding was in line with Art. 4 Paris Convention and the legislative history of these provisions.
Where there were several applicants for the first application and one of them is the sole applicant for the subsequent application, the other co-applicants must have transferred the joint priority right to the sole applicant of the subsequent application before its filing date (see T 382/07, with further references).
See also the decisions in chapter II.D.4. "First application in respect of the invention", II.D.4.2. "Identity of applicant".
The board in T 969/14 held, with reference to Enlarged Board decision G 1/15 ("Partial priority", OJ 2017, A82), that once it is acknowledged that partial priority rights exist they must also be transferable separately. This, however, has consequences for the remaining priority right, because the assignor is left with a limited right. On partial and multiple priorities, see also in this chapter II.D.5.
Source: http://www.epo.org/law-practice/legal-texts/html/caselaw/2019/e/clr_ii_d_2_2_1.htm
Date retrieved: 17 May 2021