50 C. Postal stamp "Merkur head", vertical pair with overprint "Occupied area North France" in type I, variety "inverted overprint - top down", properly franking on cover from "Ghyvelde 23.07.1940" to Dunkerque with arrival postmark on the back from 24.07.1940, rare, expertized Calves, Dreyfuß, Roumet and expertise Lothar Herbst VP (2023) "the condition is perfect. The stamps are only in small number of pieces known, therefore are they rare, with inverted overprint rare. ", Michel not listed.