It is the responsibility of the Examining Division to check whether and to what extent the priority claim is justified. However, where intervening state of the art (see VI, 5.2)) or potential state of the art according to Art. 54(3) is revealed in the search, the Search Division should, if possible, check the validity of the priority claim (see XII, 4, C-V, 1.2-1.5 and C-V, 2). Furthermore, documents showing that a priority claim might not be justified (e.g. an earlier application or patent from the same applicant indicating that the application from which priority is claimed may not be the first application for the invention concerned) should be cited in the search report (see X, 9.2(viii)). However, no special search effort should normally be made for this purpose, except when there is a special reason to do so, e.g. when the priority application is a "continuation-in-part" of an earlier application from which no priority is claimed (see IV, 2.3 and C-V, 2.4.4). Sometimes the fact that the country of residence of the applicant is different from the country of the priority application may also be an indication that it is not a first filing, justifying a certain extension of the search.

When the search is extended for this purpose, it should be directed to:

During the search for EP1, the examiner retrieved published application GB1. GB1 may prejudice the priority claim of EP1, since it was filed earlier than GB2. Published GB1 should, therefore, be cited in the search report as an "L" document according to X, 9.2(viii)(a); or

The publication US1 was found during the search for EP1. GB1 may prejudice the priority of EP1, since it was filed earlier than GB2. US1, which claims GB1 as priority, should, therefore, be cited in the search report as an "L" document according to X, 9.2(viii)(a).