The person you got it from is misinformed. Please post photos of the left side of the pistol and the front of the frame. Put a magnet on the frame; if your pistol has an alloy frame it is postwar 1963 manufacture.
Your slide bears BW acceptance marks and the above posters are correct- it was accepted in January of 1963. You gave no info on frame markings but the black plastic grips peeking int the picture also look postwar.
The BW took the P1 which is a modern copy of the P38, and Walther also made postwar pistols marked P38 at the same time, so there is some confusion by name.
Don't know where your source got the idea of 1942. What does the frame show?
The slide is clearly postwar. I don't know why you don't show us any of the frame, which may be from a different (and) wartime pistol and where some confusion might have started. Wartime HP/ModP38s were rollmarked for Zella-Mehlis, but postwar Walther set up in Ulm/Donau, as is shown on this slide.