Patras error with the control number displaced vertically: 20l ultramarine with "2" inverted with complete arch and the control number displaced vertically (Kound. 63.3.3). One sheet printed, only 3-4 copies known to exist. Stamp intact with four margins all around, two large/two narrow. Very fine for this very impressive control number error. A major rarity. (Hellas 51fNa).