While regulations for change went into effect in 1939, there were thousands of stars to be used (and used up, lost, destroyed, etc.) so they might continue to appear on caps into the 40's.
Many wartime stars appear to be two piece from a distance until you get right on top of them and see that they are one piece brass with the background enamel making the stamped in H&S seem to be separate. Ultimately you could look at the back of the star and would see the brass "stems" of the separate hammer and sickle protruding through and bent in the back of the older stars.
From an M24...hard to take good pictures this late at night
Thanks for the information on the stars. Sorry I did not refer to the listing page. I actually found this cap for sale on a different forum. Small world! :chuckle