This makes much sense. Additionally, I read in at least one source - can't remember which, canfield maybe - that these were also sent out to units for use as "field replacements". This perhaps makes sense to given some seemingly originals without rebuild markings. Anecdotally, I saw a rifle once in a shop with a scant stock that had rack numbers on the butt that looked as old as the rest of the stock, but no other markings.