Nobody really understands the breeching-up marks on No4T rifles because they weren't unbreeched during the fitting up stage - so why bother? Additionally, any sort of breeching up mark is notoriously fickle and depends too much on the fitters opinion as to whether it is or isn't aligned. (The SA80 is a good example of this.) If you need to re-barrel a No4 or a T, and I have done one or two zillion, then you don't need a witness mark...... you use the gauge or the surface plate!
Additionally, no one at H&H put the witness mark there so far as we know. What about at BSA once it was selected as suitable for TR? Good point but that'd mean it had to be stripped, marked and re-assembled again after the range test. And to achieve what?
Back to the T in question. If it was a rusty old bodged up E Type Jag that looked like it went to Italydeck cargo on a submarine, would you be happy with it? Or would you at the very least, make it presentable? What about the telescope. Should he leave the old Indian coathanger wire graticle and string crosswire? I know it's a tad glib of me to say it like this but this tired but grand old lady deserves a bit of TLC at this stage of its hard life. And the Indian markings and its equally proud heritage will still be there.