50 C. Special stamp "Congres you B. I. T. ", horizontal pair, with hand stamp overprint in type I, as properly franked multiple franking on cover from "Ghyvelde north 4-7-40", to Dunkerque north with arrival postmark on the back from 5-7-40, very fine, expertized Calves, Dreyfus, Roumet and expertise Lothar Herbst VP (2025) "the condition is perfect. The stamps are only in very small number of pieces known, therefore are they very rare. "