The Publication Manual of the American Psychological Association (APA) does not refer directly to archival materials, but the manual includes several examples of citations for unpublished materials as general guidelines. It also states that in-text and Reference List formatting for sources can be modified to be more or less specific as appropriate for different materials, keeping in mind the purpose of the citation is to direct the reader to the cited source.
See the Publication Manual of the APA, especially section 8.4 and section 10.0.
