10 on 20 Pfg postal stamp blue with plate flaw XVI " 'horizontal interrogation point' besides '0' the indication of value '20' " in the vertical pair with normal stamp, in perfect condition mint never hinged (suspending stamp unused), unsigned, in this kind especially decorative piece with the rarely only in a part of issue on field 96 occurring plate flaw, new photo expertize Gruber BPP (2019) "genuine, perfect", Michel unpriced