50 C. Special edition "Congres you BIT 1930 - Conference of the International Labour Office" with hand stamp overprint in type I, properly franked multiple franking on letter from "Ghyvelde 14.07.1940" to Dunkerque with on the back arrival stamp from 15.07.1940, in perfect condition, expertise Lothar Herbst VP (2018) : "the condition is perfect. The stamps are only in very small number of pieces known, therefore are they very rare. ", Michel 1.500.-