Datz
US Errors: Inverts, Imperforates, Color Omitted (4th ed 1992) - Loveland, CO General Philatlic Corporation
United States | Errors and Varieties -- Color | Errors and Varieties -- Printing | Errors and Varieties -- Perforation | Plate Number Coils | EFOs | Catalogs and Price Lists
US Errors: Inverts, Imperforates, Color Omitted (4th ed 1992) - Loveland, CO General Philatlic Corporation
United States | Errors and Varieties -- Color | Errors and Varieties -- Printing | Errors and Varieties -- Perforation | Plate Number Coils | EFOs | Catalogs and Price Lists