How should priority papers be marked to ensure proper correlation with U.S. applications?

To ensure proper correlation between priority papers and U.S. applications, the MPEP suggests: “It is suggested that a notation of the application number of the corresponding U.S. application be placed on the priority papers when such papers are not submitted via a priority document exchange program. Such notation should be placed directly on the priority papers themselves even where a cover letter is attached bearing the U.S. application data.” This practice helps prevent separation of cover letters and priority papers, which can cause severe problems for both the Office and applicant.