Modulex 2×4 Molds (Part 1: Colors)

There seem to be five different molds:

Old-LEGO-logo:

• A (1-14) Pat. pend
• B (1-14) Pat. pend, sometimes erased
• CA plastic, no markings (not shown, non-production?)

M-logo:

• Number below third tube (1-8) Ridge on long side
• Number between short side and tube (1-20) Ridge on short side

All molds have pip on the short side. Since the pins that make the stud hollows were so small, they often broke off, making a filled-in stud or even a peg on later mold runs.

[Original post and comments on Flickr.]