25 C. Mercury head with horizontal overprint "Occupation of Northern France" in Type I, variety "inverted overprint, block of four with common overprint across all four values as a valid postage on a letter from "Ghyvelde 07. 07. 1940" to Dunkerque with a rear arrival postmark dated 08. 07. 1940, flawless condition, the stamps are known in very small quantities, therefore they are rare - with inverted overprint very rare, certified by Roumet, Ceres and expertise by Lothar Herbst VP (2023) "The condition is flawless.", Michel 1. 100.-