1977 PLATE PROOF COB51, Exhibition Socfilex in Berlin, comp. 4 pcs of plate proofs, 3x printed stmp 6Kčs, from that 1x master die in/at definitive colors, 2x in/at brown and black color, 1x plate proof added-print on envelope, supplemented with standard envelope, all on carton paper with wide margin; good condition 1975 PLATE PROOF COB44, Exhibition Socfilex in Moscow, comp. 4 pcs of plate proofs, 3x printed stmp 6Kčs, from that 1x master die in/at definitive colors, 2x in/at grey-violet and black color, 1x plate proof added-print on envelope, supplemented with standard envelope, all on carton paper with wide margin; good condition