The filing date of the "first application" must be claimed as a priority, i.e. the application disclosing for the first time any or all of the subject-matter of the European application. If it is found that the application to which the priority claim is directed is in fact not the first application in this sense, but some or all of the subject-matter was disclosed in a still earlier application filed by the same applicant or his predecessor in title, the priority claim is invalid insofar as the subject-matter was already disclosed in the still earlier application (see V, 1.4a).

To the extent the priority claim is invalid, the effective date of the European application is the date of its filing. The previously disclosed subject-matter of the European application is not novel if the still earlier application referred to above was published prior to the effective date of the European application (Art. 54(2)) or if the still earlier application is also a European application which was published on or after the effective date of the European application in question (Art. 54(3)) insofar as the designation fees for the same Contracting States have been validly paid (Art. 54(4) in conjunction with Rule 23a).