Another Circle S, the mystery is safe, more questions!

[DonVoigt]

To add to the circle S discussion, I noticed the luger in the pictures in an auction.
Pictures are limited, but show:
Scrubbed chamber,
1921 property number applied to scrubbed chamber top,
right chamber proofs scrubbed,
Eagle 6 (inspector for Simson) applied

The description:
"Fixed sights, with "1921" on top of the chamber and the Erfurt "Crown" logo on the toggle link. An "eagle/6" proof and a circled "S" are present on the extension, with "25" on the barrel, Imperial "Eagle" on the breechblock and WWI-style proofs on the toggle links. A sear safety is installed, and a magazine well safety has been installed and removed. Straw finished small parts, checkered grips and a nickel finished magazine with an alloy base."

Is this one more "nail" in establishing a connection between the Circle S and Simson re-work? I hope to be able to bring this one home and have a better look, and an example of a "circle S".

Comments and observations, please.