unmounted mint (18c) Bicentennial souvenir sheet, 'USA/18c' omitted, imperforate, untagged (1687k), never hinged, light natural offset on reverse (exists on every known example of this error), light printer's fingerprint in T. margin (occurred during the printing process), otherwise very fine, very rare, only about twenty are believed to exist, Datz states 'very rare', Scott retail $3,000.00 photo