"If you assume that the production was relatively steady from 1915 to 1942, (which is a big assumption)"
That is a big assumption, and an incorrect one. During the depths of the depression production fell off to a fraction of what it had been in the 1920s as sales were non-existent.
When S&W began gearing up to produce firearms for the British in 1940, one of the big selling points after the Light Rifle debacle (the Brits wanted their $1 million R&D investment back, S&W didn't have it) was that the company could produce a LOT of revolvers in a very short period of time because they were sitting on huge stocks of parts that had been made in the late 1920s and early 1930s before sales tanked.
It's very difficult to say with any certainty when a particular revolver was made during this period.
"The gift which I am sending you is called a dog, and is in fact the most precious and valuable possession of mankind" -Theodorus Gaza
Baby Jesus cries when the fat redneck doesn't have military-grade firepower.