Hello,
Marvelous!
I was out for some days and couldn't discuss with you. Sorry!
And my English is not so fluent, so I will only do some remarks.
1- It seems evident for me that a Fed S is only a S with its 2/50 lens. And I don't see on eBay lots of S with 3,5/50: only one now exactly. So I thought till now that number of 2/50 = number of S. But of course, no proof!
2- The Princelle notes that S are possible for c and d series only. But some Berdsk-S can be registered. I own one in the 181000 which seems to be true. But no proof once more: it's so easy to take an S in the 150000 and to put the cover of a Berdsk....
3- In my opinion, there were some rare Berdsk S really made (I have traced 6 bodies, including mine). After WW2, the factory had real problems to begin again production, and all the possible spares were certainly used. Why not from S coming from d-series? And more: the 1/1000th shutter of some Fed-Zorki certainly come from S shutters: KMZ didn't make such shutters for their 1...
4- I tried to classify S bodies and 2/50 by pairs. Each time I had seen an S, I asked for the # of the body and the lens. I hoped that the first body(c. 56000)had the first lens(c. 21000) and the last had the last one (c. 33000)and so on inside. What a disappointment when I noticed that ten pairs out of 30 only were "on the line"or not far! All I can tell -but I think it can be important- is that almost all the first half of S bodies (c. 56000 to c. 115000) have lenses from the first half (c. 21000 to c. 27000), mutatis mutandis for the second halves. As if the 2/50 lenses had been made in two batches corresponding to two different periods, for example early 1938 and end 1939, stored, and taken when necessary.
5- About Berdsk (the plain one, not S), I cannot be more precise than Aidas. I have a plain one with # 182912 and I never saw a number exceeding 184000.
6- About 2/50 lenses, the individual serial number is a thing, but what about the batch? In fact, what is a batch for prewar Fed lenses? Of course, it can be a global number common to a certain number of lenses. OK. But I was also said that it was the mark of the workshop which made them. OK. Lately, one of my friends told me that it can be the number of a secret factory: optics and armament depend on military secrets. Kalashnikovs are numbered in such a manner! OK again. What else??
7- If I have a look at my lenses, here are the numbers and corresponding batches:
- 21488: 105. This one is a fake Summar true 2/50 Fed lens.
- 22001: 32,
- 26708: 74-7,
- 27890: 41,
- 29044: 59.
No arithmetic reason in these numbers...
And I don't understand the number given by Aidas. Perhaps only the batch?
I stop now. It's already far too long!
Amicalement.
Jacques.
PS: really thanks for your #. If you could give me those of your extra lenses (including the 3,5/50 macro I had forgotten in my first mail), don't hesitate!
I could argue forever Bill... hehehe 
