[Edward Tinker]

I expect most things 'out of place' to be done post war. However, It is also possible grips were replacements during war. An armorer or repair facility would use whatever grips, magazine bottoms, other parts as needed; so you can find odd mixtures at times and they are perfectly legit.

But unless something was brought back by the GI (and you know how many folks forget they added a police holster because it was in excellent shape, or whatever) that is the only way to know it came that way.