Can the frame be attributed to DWM as well as the 1920 dated receiver?
Yes
What is the term "aya4" as describes the proofs?
Sorry, a typo. It should be WaA 4 or ArA 4.
The proofs on the right front of the receiver are post WWI Dove or Eagle ( Turkey ) proofs due to their appearance, both can be found on 1920 dated Lugers. Actually more of a Peace Eagle (wings folded) ArA 4 or WaA 4 below the eagles is the code used only on 1920 and 1921 production Lugers. Most likely to indicate non-war time production.
The proofs will help distinguish a 1920 date from year of production, or a Gov't property mark, also 1920. When these proofs are present, it will be a 1920 production Luger.
Are these proof marks the same as number 31 on page 3 of the proof mark references?
Not sure. I've never seen that publication. Here's a photo from Jan Still's "Weimar Lugers".
Does the Mauser toggle suggest a World War II rebuild prior to any East German rework?
Most likely an East German replacement. They used any part that would work without concern for matching parts. Pre EG German armorers were more stringent in using the correct parts.
So this is not a so-called "sneak" variation which is how it was described to me once?
No, "Sneaks" were made by BKIW (transition between DWM and Mauser) beginning in 1929. All "Sneaks" are found with a DWM or a Blank(unmarked) toggle. "Sneaks"( a marketing ploy coined by an American dealer to add mystique) were not being sneaked as has been suggested. Most likely just made up from left over, and unmarked parts. DWM (BKIW) was stuggling to stay in business and was doing anything to maintain production.
Didn't the Treaty of Versailles have provisions that regulated production of the Luger in 9mm in 1920?
Probably not. The Allied Commission had more important things to do than count Lugers.
DWM began producing Lugers for commercial / export sale in 1919.
Approx. 40 to 50 thousand 1920 and 1921 new production Lugers in the no suffix, a and b suffix range were procured for the Police, and approx. 8 to 10 thousand in the same SN suffix blocks were procured for the military.
How long did Lugers see service in East German hands after World War II?
Well into the 60's, and possibly 70's and 80's.
Do the incomplete markings which appear to be E C C S A indicate an importer?
Yes
Does anyone recall the batch of Lugers coming in to the USA in the mid 1980s and advertised in the "Shotgun News"?
This is probably one of those.
Manufactured in 1920 for military consumption.
Saw service through the rise of the Nazis to power and through World War II (possibly undergoing a rework).
Likely captured by the Soviets, either on Eastern Front or in stores elsewhere.
Given as material to East Germany to arm police or security forces and reworked at that time.
I'm guessing that sometime prior to 1985 it would have had to pass from East German ownership to a third party in order to have been imported to the USA.
That's pretty much the story.
Hope this is helpful?
Ron