50 C. Special edition \"Congres you B. I. T. 1930\" with overprint in type I, overprint inverted, properly franked multiple franking on letter from Ghyvelde 14.7.1940 to Dunkerque with on the back arrival stamp from 15.07.1940, 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. Multiple franking with special stamps and inverted overprint are especially rare. \", Michel 2.000.-