unused Block of Four 6c-24c 1918-23 Air Post (C1-C6), 63 unused stamps comprising C1 (five), C2 (eighteen), C3 (seventeen), C4 (nine), C5 (five), C6 (nine), most in blocks of four incl. three arrow blocks, three with plate no. and one center line block, 25 stamps are never hinged, others generally lightly hinged, a few have back faults, otherwise fine-very fine lot, Scott retail $6,850.00+