Hello and thanks for the question.
Allow me to begin by saying that I'm not an expert. However, I may be able to add a little bit of information that you may not have found yet.
First, the "Neuwtadt A/H" is the name of a city in the area of the Rhineland-Palatinate, and frequently referred to as being on the German Wine Route or "an der Winstraße." The "A/H" is a reference to "an der Haardt" with "der Haardt" being one of the subdistricts of Neustadt.
Second, there are lots of references to Paul Erdelt and firearms with his name on them on the internet. Most of them can be found with a search for "P Erdelt" or "Erdelt Neustadt". The majority of the weapons appearing with the Erdelt name seem to be shotguns, but there has been at least one pistol sold by Rock Island in 2009 with his name on it.
https://www.rockislandauction.com/d...shot-breechloading-flobert-type-target-pistol Several times people have emphatically stated that Paul Erdelt was not a gunmaker but rather just a sporting goods retailer, saying that he sold guns manufactured by others with his name on them much like the early 20th century hardward stores in the U.S. offered. Other folks just as emphatically state that the company was in business from 1889 to 1945. Unfortunately, there is no evidence, documentation or proof of any of this. There are some vague references to Frank De Haas, who was the authority on single shot firearms for many years. I no longer have any of his books to check, but even if I did have them, I wouldn't put a great deal of faith in any of the history I found there. De Haas was pretty good on technical information, but he wasn't as accurate when it came to history. When I find situations like this, I always suspect that bad information is just getting passed along as if it were undisputed fact, when it reality it is largely just hearsay. The only fact that I've found is in the form of an old postcard from the period 1900-1920 of a street scene in Neustadt A.H. which shows a façade of businesses with one business displaying a sign "Paul Erdelt Büchsenmacher" which translates as Paul Erdelt Gunsmith.
https://www.ebay.ie/itm/52473870-Ne...935344?hash=item48a92cde70:g:1l8AAOSwgkhalA~0
Third, as has already been explained, it would not be stainless.
Fourth, the folks over at the German Gun Collectors Association ( germanguns.com ) are always helpful and have a pretty nice forum where you should find more definitive information.
Thanks again for the post and keep us informed on what you find.