50 C. Postal stamp "Merkur head" with overprint in type I, horizontal pair with overprint, properly franked more franking on cover from "Ghyvelde 2.08.1940" to Dunkerque with reverse arrival postmark from "3.08.1940", very fine, expertise Lothar Herbst VP (2018) : "the condition is perfect. The stamps are only in very small number of pieces known, therefore are they rare, Michel 400.-