I now it's after the event but I asked the old eagle eyed In-Inspector about what he'd do with this hand stamped body. Because stamping a No4 body was a complete no-no. Big Robbies reply says that thousands upon thousands of badly stamped, etched or scratchy-pen or otherways marked bodies passed over his bench. He'd just add to the in-inspection work sheet '....linish clean markings and re-engrave according to EMER....' (or other common practice). It was common to do it on feintly marked Sterlings, Stens, Berridge signal pistols, No4's, L1A1's etc etc. So long as the same marks were being applied there wasn't a problem at all.

That seems to be the answer. And when you think about it, that's just what happened with No4's being re-engraved to L42 or L59 where you can still occasionally see the old markings or signs of the linishing wheel