https://en.numista.com/catalogue/pieces105.html
The KMB has a smaller (by about 10%) reverse design.
KMB = Kleines Münz Bild [petite pièce de monnaie / small coin]
I found this first image, and the KMB is on the left - notice lower left where the design is further away from the border ...
and is on the right in the second image, found further down on this page (in French) ...
http://eurorare.blog.mongenie.com/index/tag/KMB