20 Kop. vertical pair in block of four!, marginal and corner examples, imperforate between! Genuine Cyrillic "PSKOW -k- -2 1 42" cancel! Almost unknown used! Upper left stamp with plate flaw I, major area rarity, unsigned! Photo certificate Walter Zirath BPP (2025): "Condition is sound. Only a few pairs are known.", Mi. -.-, as practically never offered!