It is not uncommon for a GI gun to have mis-matched parts. Armorers didn't care about collectibility. Their priority was to service and return a working gun to the gun on the front line. Even at the arsenal level, no nicety was practiced in matching parts. That wasn't even a consideration to them. Your M-1 Carbine is one such critter.
Vigilantibus et non dormientibus jura subveniunt. Molon Labe!