There is a wide variety of magazine variations, more than P38 pistol variations.For a good overview on the production process, development and variation of magazines I recommend our book more information.
In total four manufacturers of P.38 magazines are known.The following waffenamt acceptance stamps can be found on the mags (sometimes the mags have no stamps at all!):
-Mauser (E/135 early) (E/WaA135 late)
-Erste NordBohmische Metallwarenfabrik (E/706 and/or jvd)