When in 1957 did they stamp Model 10

[pbsodetective]

I am trying to date an M&P Serial C3817xx. I have seen that # quoted as both 1956 and 1957. The gun is 2" square butt nickel with a full moon front sight. The gun does not have the serial number on the cylinder, barrel, yoke or extractor star that a 1956 should have gotten during "soft fit" at the factory so it was assembled after May 1 1957 when "soft fit" was eliminated at the factory. There is no model # stamped inside the yoke. My older brother was looking for a gun made in 57 (his birth year) and I reminded him of Aunt "E"'s gun.I live in Fla. and he and the gun are in MI. I had him look for the #'s and they are not there. When S&W starts taking letters again we can get a letter. Is it known what month they started stamping Mod 10? Any one with a lettered serial close to help date this one? Be nice if he could get his 57 from "family".
My Great Aunt got the gun when she became a widow and it was under the extra pillow on her bed for the next 35+ years (it is mint), but no box or papers. When her children did not want it my father got it from her.

[DWalt]

Generally, model marking started showing up in 1958 shipments. Model designation stamping was ordered on June 12, 1957 and Model 10s allegedly were first stamped in September 1957. C3817xx was almost certainly manufactured in mid 1956, or possibly earlier that year, but was likely to have been shipped sometime later in 1956 or even early 1957. In any event, yours should not have the Model stamping in the yoke area, so it is a pre-Model 10. Looks like you need a factory letter if you need proof positive it was shipped in 1957. Best anyone can say is that it could have been.