I've just managed to find the "wiki" page that this forum has, which lists various Soviet photo equipment. It can be found by going to the forum Home Page and looking down to find:
"wiki catalog and resources issues/questions, then
Well I was going to give a set of instructions on how to find the list with that camera in it, but I can't find the bit I clicked on to get to the list, lol. Anyway, I already had the list page open in a different tab, so I'm going to try and post a link to that page:
http://ussrphoto.com/wiki/default.asp?ParentID=1For the listing of the FED 3L/D that they have, it doesn't have a serial number on the back either, but they don't show the underneath. I presume it does have a serial number there.
Let's hope someone who knows why there's a difference in the placing of the serial numbers on some FED 3's and why there is a difference in the length of the serial numbers on some FED3's, will answer soon.