I had a Pre-40 serial # 248 & it was made in 1953..
This gun had four sideplate screws & still had the pin in the grip in the stash spot to deactivate the grip safety..
S&Ws "Centennial" year was 1952 & that pistols frame shape was named after that..
The M42 was the same except it was an Airweight..
You'll have to contact S&W to be sure but would guess 1953-1954
Here's a pic of the one I had, on the right on the red gunrug..
The rest are S&Ws & Ruger SP101s