Hello, I received some days ago an early Fed 1b (#7122, without accessory clip). Like a 1a, but with the YCCP engravings.
The lens is a 1 turn (in fact, 310°) with four slots to unscrew the front lens. It has three engravings (844, just behind the infinity lock, 662, and 122: at the reverse of the infinity lock).
Pegorari says that the number of the lens follows more or less the number of the body. It's the case for my 1a, but not for this 1b.
More: if we compare the numbers, it seems that 122 is the end of 7122. Leitz used this numbering for their I(C) non standard: the lens of my 1930 C Leica is numbered 935 and 48935 for the body. All that to show that body and lens were adapted together at the factory.
Could it be the same for Fed? But why not for my 1a? But we know very little about standardization at Fed's. Or would it be luck only?
Another curious discovery: the screw seems sawn, as if to facilitate the screwing of the lens to the body.