50 C. Special edition \"Congres you B. I. T. 1930\" with overprint in type I, properly franked multiple franking on cover from Ghyvelde 3.7.1940 with on the back arrival stamp from 4.07.1940, faultless preservation, expertise Lothar Herbst VP (2019) : \"the preservation is perfect. The stamps are only in very small number of pieces known, therefore are they very rare. \", Michel 1.500.-