PCT International Search and Preliminary Examination Guidelines
PART III EXAMINER CONSIDERATIONS COMMON TO BOTH THE INTERNATIONAL SEARCHING AUTHORITY AND THE INTERNATIONAL PRELIMINARY EXAMINING AUTHORITY
11.24 It should be noted that the “relevant date,” for the purpose of considering prior art, is defined in Rule 64.1(b) as meaning the international filing date or, where the international application contains a valid claim to priority, that date of priority (see also paragraphs 6.03 and 6.04). It should be remembered also that different claims, or different alternatives claimed in one claim, may have different relevant dates.
11.25 The questions of novelty and inventive step must be considered against each claim (or part of a claim where a claim specifies a number of alternatives) and the prior art in relation to one claim, or to one part of a claim, may include matter which cannot be cited against another claim, or part of a claim, because the latter has an earlier relevant date. Of course, if all the matter in the prior art was made available to the public before the date of the earliest priority document, the examiner need not (and should not) concern himself with the allocation of priority dates.
11.26 The validity of priority dates for a claim or a part of a claim is considered in detail in Chapter 6.