So, since they have serial numbers, all 1911's were made in Utica?
Yes. these were made before Savage acquired Stevens in 1920.
From what I can find Stevens was ran as an independent fully owned subsidiary until about 1930 when they started to become just a brand name. In the 1929 Savage catalog there were no models listed that also had a Stevens, Springfield or House branded version except the Model 29 pump 22 (the exception). In 1931 you start to see to see Savage, Stevens, Springfield and House Branded version of the same design 22's, none of which were serial numbered and all having the same type inspection stamps. The Model 1904 (by then cataloged as the Model 04) was dropped in 1931, they had always been serial numbered. The 1931 catalog is when the Model 28 pump shotgun was dropped and the Model 720 shotgun appeared, not sure where they would have made it, a Savage catalog has a picture of a worker bluing a receiver but the picture could have been taken at the Steven plant.
The inspection stamps - about the time of the Savage Arms purchase Stevens started using different style inspection stamps, these consisted of round symbols and circled numbers or letters all about 3/16" diameter. These changed over the years and sometimes guns can be given a rough date from the inspection stamp. The same stamps are found on all the Savage 22's made after 1931 and they are on the couple of 220 shotguns I have. Use of these seemed to have stopped after WWII or when Savage moved. I never started documenting the inspections stamps until recently. The exceptions is the Model 29 pump & it's versions.
The Model 29, 29-A & 29-B - There are versions of the 29 & 29-A branded Stevens, Springfield as well as several house brands. These all appear to have been made at the Utica plant. None have the Stevens style proof marks and all a serial numbered. The Stevens versions of these are the only Stevens 22's from that time to have serial numbers. I got some information from John Callahan several years ago that the 29's started with three different serial number series and then were combined into a single series starting in the 18,000 range, he never said, but I assume these were all in then in the same ledger, I never thought to ask. This is when the use of a letter after the serial number started for the Savage and Stevens version, the house brands always had a 'K', the Savage's were followed by an 'L' and Stevens by an 'M' - the use of 'M' for Stevens didn't last long, a few high serial number Model 75's have it, later Stevens & Springfield versions had a 'K' like house brands.
I'm sure John Callahan would have better information about all this, wish I would have asked when he was still historian.