#1. Buy the gun, not the story.
#2. With antique firearms, condition drives worth MASSIVELY. The difference between a 10% gun and an 80% gun is about 1,000% of the value.
You need to ask, how did the seller come to be able to obtain the provenance (documented history) of the gun? Is he a serious collector, a dealer in antique arms- or he is Joe Schmuck? I know one dealer that if he told me he had Bobby Lee's personal belly gun, I would believe it without seeing it. Know another "dealer" I would not believe if he had a photo of Sam Colt holding the gun.
In doubt, see #1 above.
What we have here is... failure- to communicate.