Peter, excellent, thank you. You have confirmed my thoughts on about 50%, which is great.

Apologies for asking about the sight now, when I read the fist word of your reply sentence the Homer Simpson moment occurred. Of course it is the component number, per the drawing. A little embarrassing that one.

Glad you confirmed the original maker as BSA Shirley. I'm still baffled by the many variations in markings and lack of consistency. I guess that was symptomatic of limited skilled workers, staff turn over and constant supply problems which lead at times to staff reassignment and re-starting work some days later with another crew. I guess we fall into a modern trap thinking manufacturing standards expected now were the same under wartime conditions. I'll park those thoughts from now on.

Just a thought on the over stamped proofing marks on the nocks form. I can imagine the double strike, but the over stamping of the relatively large "C" seems a little inconsistent. What would that mark be likely to indicate? IS it likely to have been done at the same time as proofing?

Learning about these details is a convoluted process, and the references I've had access to seem to only touch the surface and possibly muddy the waters with the impression that what they state "is so" when it's only part of the story.

Very grateful for your kind assistance, thank you.