25 C. Postal stamp \"Merkur head\" with overprint in type I, horizontal strip of four - left pair without overprint, right pair with overprint - this inverted, properly franked more franking on letter from \"Ghyvelde 29.07.1940\" to Dunkerque with reverse arrival postmark from \"30.07.1940\", faultless preservation - few perf tips tiniest shaded (insignificant), expertise Lothar Herbst VP (2018) : \"the other preservation is perfect. The stamps are only in very small number of pieces known, therefore are they rare. In this variety \"pair with overprint\" and \"pair without overprint\" is the franking very rare. \", Michel 1.500.-