I'll be at Purdey in a week and can ask them what they do, or if they have had a common practice, but Purdey was just my example.
I've seen hundreds of rebarreled guns. I haven't check the numbers on all of 'em.
Guess I'm looking for first-hand knowledge to prove guns have numbers different from the barrels - when barrels have been replaced by the original gun maker.
Again, I'm talking English Best, which I define as the holy trinity of Boss, H&H, and Purdey - alphabetical - not the order I think they rank. ;-)