Important Postal History Items. RSFSR - SOVIET UNION MIXED FRANKING COVER: 1923 (December 3), cover from Novocherkassk (Don Obl) to Dresden, franked by three RSFSR definitives (two on reverse) and six Soviet Union values (all on reverse), all appropriate markings, Dresden ''12.23.12'' date stamp cancellation on all RSFSR adhesives (they were not cancelled in Novocherkassk), mostly VF, N. Mandrovski certificate, Est. $500-$600 (Image)