36th International Auction- part 2- philately & picture postcards

1966 (1.2.), formular airletter bearing optd. 6d stamp used from Bulawayo to England with green cachet 'STAMPS NOT VALID' and violet boxed 'UNDELIVERED FOR REASON STATED / RETURN TO SENDER' with tax-markings and british 1s. postage due cancelled 5th Feb. 66 and boxed 'charge not collected' handstamp, and additional a formular airletter front with two Rhodesia stamps used from Causway to England with postage dues used on arrival and green boxed 'STAMP NOT VALID / TO PAY......' and affixed label on front about 'no legal basis for Rhodesia stamps', unusual pair