50 C. commemorative "Congres du B.I.T.", horizontal pair with Type I handstamp overprint, correctly rated multiple franking on letter from "Ghyvelde Nord 4-7-40" to Dunkerque Nord, arrival 5-7-40 on reverse, perfect condition, expertised Calves, Dreyfus, Roumet and expert report Lothar Herbst VP (2025) "Condition is sound. These stamps are known in very small numbers, hence very rare."