If the applicant proves to the satisfaction of the EPO that the international filing date is incorrect owing to an error made by the receiving Office or that the priority claim has been erroneously considered not to have been made, and if the error is such that, had it been made by the EPO itself, the EPO would rectify it under the EPC, the EPO must rectify the error on the applicant's request and treat the international application as if it had been accorded the rectified international filing date or as if the priority claim had not been considered not to have been made (see also E‑IX, 2.9.1).
Further, if a receiving Office accords the international filing date on the basis of incorporation by reference of missing parts under Rule 20.5 PCT, the EPO as designated/elected Office will review of its own motion whether the requirements of Rule 82ter.1(b)(i)-(iii) PCT have been complied with. In particular, the EPO will consider whether the element or part incorporated by reference was indeed missing. For instance, where the international application contained a description and a claim or claims on the international filing date, it is not possible to replace these elements with elements from a priority application. It is also not possible to add elements from a priority application if this would result in the international application having, for instance, two (or more) descriptions or two (or more) sets of claims. As of 1 July 2020, such cases may however be handled by the receiving Office under Rule 20.5bis PCT (see E‑IX, 2.9.4 for the determination of the filing date in such a case).
If the EPO does not agree with the finding of the receiving Office, it will notify the applicant that it intends to consider the (later) date on which the missing element or part was furnished as the international filing date in the European patent grant procedure, giving the applicant the opportunity to comment in accordance with Art. 113(1). In the case of missing parts, the applicant may also request that the missing part concerned be disregarded in the European patent grant procedure. In that case, the missing part will be considered not to have been furnished and the EPO will not treat the international application as if the international filing date had been corrected.