Evan:
Possibly, but that has no bearing on this thread, which I pointed out.
With regard to your .375, if it has no bolt safety, it was originally of early Metford pattern. UNLESS, if you remove the fore-arm, there is a tiny hole drilled across the rear of the lower receiver, which is where the cross-pin would fit if it had the Patent tang safety. If it does, there should be somewhere on the action, normally hidden by the wood, in very small letters, #1 (or No. 1) PATTERN, stamped, if it was meant to be sold as a "named" retailer. I have never seen a B.S.A.Co. retailed rifle thus marked, although EVERY #1 retailed by a "maker" I have seen was.
Is your receiver engraved in the same manner as the magazine? If so, I would hazard a guess that it originally came with the rifle, which would make it 3 of 175 rifles I have knowledge of [98.8%]. If the receiver is not engraved or engraved in the same manner/pattern as the magazine, then it was swapped out since it left Brum 'lo those many twelvemonths ago.