50 C. special stamp "Congres you B. I. T. 1930" in the horizontal pair from right margin of sheet with overprint in type I being a correctly franked multiple franking on cover from "Ghyvelde 23. 7. 40" to Dunkerque with reverse arrival postmark from 24. 7. 40, signed Dreyfuss, Roumet and photo expertize Lothar autumn VP (2015) : "the condition is perfect. The stamps are only in very small number of pieces recorded, so that they very rare are. Multiple franking with special stamps are extraordinarily rare. "