50 C. Postal stamp \"Merkur head\" with overprint in type I, vertical pair with overprint, variety \"inverted overprint\", properly franked more franking on cover from \"Ghyvelde 31.07.1940\" to Dunkerque with reverse arrival postmark from \"1.08.1940\", faultless condition, expertise Lothar Herbst VP (2018) : \"the condition is perfect. The stamps are only in very small number of pieces known, therefore are they rare, with inverted overprint very rare. \", Michel 800.-