50 C. Special stamp \"Congres you B. I. T. \", vertical pair, with hand stamp overprint in type I, variety \"inverted overprint\" as properly franked multiple franking on cover from \"Ghyvelde north 26.7.40\" to Dunkerque north with arrival postmark on the back from 27.7.1940, faultless condition, signed Dreyfuss, Roumet and expertise Lothar Herbst VP (2018) : \"the condition is perfect. \"