In the late 1930’s Montblanc introduced their new numbering system for pen models. This consisted of a three-digit number, sometimes with an additional letter at the end. This model number can be “read” if you know how to decode it.
The first number is the price category
1: Meisterstück or Masterpiece
2: Medium priced
3: Economy Model
The second number indicated the filling system
The third number is the size of the nib.
Occasionally, a letter would follow, indicating the finish and colour
E: Chased rose pattern
PL: Silver grey / Black
The above info excerpted from Fountain Pens of the World, by Andreas Lambrou, published by Classic Pens Ltd. If you are interested in fountain pens, you should own this book!
There was an additional discussion at the fountainpennetwork.com forum regarding the meanings behind the last letter. The discussion started as a debate as to whether “G” stood for “Gold nib” or “Glatt (Smooth) finish”. Reading this discussion, it seems that it can be concluded that the meanings of at least some of these letters were different in different time periods – and that there was no fixed system.
The following was posted to the forum on this page:
According to the 1936 MB catalogue:
G = Glatte Ausfuerung (High Gloss)
S = Schraffiert (Hatched / guilloche chased pattern)
E = Rosenmuster (Engraved rose pattern)
PL = Platinschwarz (Black & silver striated)
P = Perle (Black & Pearl)
K = Kurz (Short version)
One additional interesting piece of information from that forum discussion is the mention of a “JB” imprint on some vintage Montblanc pens. This stands for Jawahiri Brothers, who were the exclusive importers of Montblanc to India in the 1950’s.