40 Pfg postal stamp with overprint "C. I. S" with plate flaw I the original stamp "I in Slesvig almost missing" inside a blocks of four with three normal stamps, in perfect condition mint never hinged, Mr. Vossen attested the piece already 1977 perfectly quality and accented the rarity, there at that time only 4 copies recorded samples, as many copies like it today be - surely is the number of pieces still manageable, current photo expertize Gruber BPP (2016) : "the stamps are genuine and in perfect quality. ", Michel - . - being a block of four surely unique!