I can only speak for the gunmakers pre WW1:
I think we are looking through the lens of people who are interested in preserving these guns for eternity.
This was not the gun makers aim in the C19th and early C20th: they needed re-orders and repairs to keep their men working, restocking and re-barrelling were not just a service to their clients, they were good earners.
We see the effect of 100+ years of oil soaking, they really didn't intend the stocks to go beyond the use of a single user/owner, perhaps 50 years, more likely replaced or 'handed down' by 10-25.
Getting a really special gun restocked or rebarrelled was not a big deal financially. Most of the owners of quality guns were wealthy, some very wealthy, and labour was cheap.
You only need to look at the significant number of modest boxlocks that have been rebarrelled to see the effect.
I suspect that the number of guns that we assume to have 'original' stocks is far smaller than generally thought.
