One hesitates to say "never" in the S&W world. However, I have not seen, nor heard of, any postwar commercial .38 M&P that was sent to a distributor, police department or individual with smooth wartime stocks. None show up in my database.
The one you own (SV809351) is clearly a postwar commercial example (plugged swivel hole, etc.). The highest number that shipped to the Navy is SV802722, which shipped on August 13, 1945, to the Norfolk Navy Yard (note the significance of that date!).
Moreover, it is in the range of a large shipment that went to the NYPD in early 1946. I don't find that number listed in that shipment, but SV809352 and SV809354 are on that list. I have very little doubt that the stocks you describe are not original to that revolver.
I suspect, as you do, that someone put them on the gun later.