30 C. and 70 C. postage stamps "Mercury Head", with a horizontal hand-stamped overprint "Occupied Territory Northern France" in Type I, as a valid mixed franking on a letter from "Dunkerque 8. 07. 40" to Ghyvelde with a reverse arrival stamp dated 9. 7. 40, flawless condition, examined by Calves, Dreyfus, Roumet and expertise by Lothar Herbst VP (2025) "The condition is impeccable. The stamps are known in very small quantities, therefore they are very rare.", Michel 800.-