50 C. Special edition \"BIT 1930 - Conference of the International Labour Office\", vertical pair with inverted overprint \"Occupied area North France\" in type I on cover from \"Ghyvelde 25.07.1940\" to Dunkerque with arrival postmark on the back from 26.07.1940. Expertized Dreyfu+?, Roumet and expertise Lothar Herbst VP (2023) \"the condition is perfect. The stamps are only in very small number of pieces known, therefore are they very rare. Multiple franking with special stamps and inverted overprint are in this ensemble especially rare. \", Michel 1.200.- plus