Just because none of the prime contractors produced all of their own part doesn't mean there's no such thing as an original carbine. They all had a chain of subcontractors for a reason(s), if that sub provided parts to one of the prime contractors then there's a chance a carbine as it left any given prime is original. Can you imagine how few carbines would have been built if all of the primes had to make all of their own parts? That would have given the term inefficiency a whole new meaning.