Hello FUJINON, An older post here of yours, but I’m in the same situation and doing some research on a ‘war-time’ IIIb I have. I was wondering if you still have the camera and found any more information. My camera is ser. No. 349639. In very excellent condition (only some light chrome scuffs on the back edge top plate from a case, and some light scuffs/scratches on the bottom plate), with the smaller tripod socket baseplate. I wrote to Leica Wetzlar and they were happy to give me their record of the camera;
"Many thanks for your request.
The SN. 349639 was delivered on 24.4.1940 , the place of delivery or recipient is not noted.
No entry in the old maintenance/repair books for this serial."
The Nazi government banned all exports of 'vital military equipment' including cameras I found in the early part of 1940, a couple of months before this camera entered the records. Leica cameras were valued for export as foreign currency exchange before this. It may have been intended for export (the smaller tripod socket), but what happened after that is a mystery. It probably was not used by the German military if only because there is no Fl. top plate engraving, and survived the war in almost unused condition. My speculation is it may have been sold in a Nazi-occupied country, or even in Germany, and 'hidden way' and so not used much. Or even maybe keep at the Leitz Factory/employee because the "place of delivery or recipient is not noted."
It has the original pre-war fine-silk shutter curtains in good condition, the finder is clear, and RF split image is bright, camera's leather covering is very good. The camera seems to have spent most of its life in a case, has not been used very much at all, and needs a good cleaning of the old lubricants as the shutter speeds are sometimes off/sticky, otherwise, it is a very beautiful camera. It's 84th birthday is coming up in 2-months!
It came to me a couple of years ago. I've always wanted a IIIb, the last version of a somewhat rare original smaller body Leica, brass shutter cage, and with a few improvements; closer RF and viewfinder view, diopter adjustment location, 4-screw spring accessory shoe, and brass lens mount stiffeners (for a couple heavier lenses Leitz had introduced). It didn't come with a lens, but I have an early 1938 pre-production run of a 5cm Summitar with a 'bar-door' hood that looks great on it, and at some time Leitz applied lens coatings to this lens so its performance is very good.
That's what I've found, theories on the camera.
Best
