For purposes of this subsection, "publication" means printed paper material, including without limitation newspapers, magazines and trade journals and employee, client and organization newsletters, issued at average intervals not exceeding 3 months 7 days that manifests a continuity of identity from issue to issue by a front page masthead bearing the name, date, volume and issue number of the publication and by a continuity of style, format, themes and subject matter. For purposes of this subsection, "publication" does not include printed paper materials consisting primarily of advertisements or the promotion of a single seller's products or services.