The applicant may correct the declaration of priority within 16 months from the earliest priority date. Where the correction causes a change in the earliest claimed priority date, this time limit is the earlier to expire of:
However, this time limit cannot expire earlier than four months after the date of filing. Thus, if the originally claimed priority date is incorrect and precedes the date of filing by more than twelve months, the applicant will always have at least four months to correct this date, i.e. the same period as if he had claimed the correct priority date (and for example got the file number wrong) and claimed a full twelve-month priority period.
If the applicant files a request for correction later it may, exceptionally, be allowed if it is apparent on the face of the published application that a mistake has been made (see A‑V, 3 and other sources therein).