another gun with serial number 39520X shipped in 1922. I would agree that your revolver would have likely shipped after the change in stock design. Those stocks show much more wear than the gun unless there was a re-bluing done at some time during its life. Is there a remote possibility that the factory found a set of gold medallion stocks two years after the switch to plain convex stocks, probably not. A factory letter might answer the question, but might not. Look at the pencil marks with different light sources at different angles, with magnification and you might identify a couple of the numbers??
Over 100,000 K frame 38 M&Ps were shipped in 1920 alone and during the early 20s, they were hot sellers and went out the door as fast as they were made. By the mid-1920s sales slowed and almost stopped after the Stock Market Crash of 1929. Still, about 300,000 38 M&Ps were shipped in the 1920s. The last revolver documented in the SWCA database to ship in 1921 was around 390,000. Bottom line is that it would be unlikely that there were any of these stocks left after over a 100,000 went out the door in 1920.
The attached image shows the stocks that would most likely have been original to your revolver.
