Hallo Tim and all...
Reference post #18, there is a nice site on the web to look for little details like that.
LE PLANCHAGE DES BLEUS DE FRANCE
These folks put a treamendous effort in this. Plating stamps to original Plate is a longue process on many decades. A large amount of work was lost in these processes because of non publication (Older generation collectors). Thankfully this site exist.
Salutations
Sylvain