This is just a "for what it's worth" comment, but I really doubt that the guns in the real old West stayed looking as pristine anywhere near as long as they do today, at least if they were being carried and used much at all. Reading stories about individuals hunting in Alaska (no doubt one of the toughest conditions on firearms out there) the author always adds comments about how impossible it was to protect the guns, even stainless firearms suffer. Most of those hunts are relatively short term - one to two weeks at most, and pictures of relatively new firearms show the abuse clearly, in spite of claims of complete stripdown and thorough drying out and preservative applications of various oils and specialized lubricants - or as Popeye would say - "Lubrikinks." I can only imagine that the abuse of holster carry in a permanent state - I doubt that many of the folks who carried on a regular basis took their guns out of the holsters much except for cleaning or shooting - was pretty detrimental to finishes. Consider first of all the nature of leather and its ability to hold water, and then add in the fact that if a gun was fired and put back in the holster, there was a continuously growing residue of black powder building up in the holster, and impregnating the leather. What's that going to do after getting caught in a rainstorm or even in extremely humid weather!? I realize that much of the West is drier than the East in terms of humidity, but any "using" guns, handguns or rifles or shotguns in scabbards, or leather cases were subject to considerable abuse. I've read of situations where guns were unable to fire due to rusting up of internal parts - not the norm I'm sure, but...
Most of what we do with guns today is pretty casual in comparison, yet on the relatively few times I carry a shotgun out, turkey hunting, deer hunting, grouse, rabbit and squirrel hunting, I can wear off the bluing at the carry point in a couple of years. Yes I do keep my guns clean, so even steel receivers are not allowed to grow any ruse, but the finish is polished off. What would happen to a gun carried daily and subject to the wear and tear of relatively poor fitting holsters, especially while bouncing on horseback, not to mention a rifle in a saddle scabbard? Again, rust might not be allowed to grow, but the finish is going to go, and it isn't going to take as long as it does today.
Finally, while firearms were important, they were probably treated with as much concern as some people invest in their cars today. There are those that you chase in order to buy their used vehicles because you know they're prime, but others? Care is important, yes, but hey, why change the oil before the light comes on? It sounds stupid, but people do it. Even intelligent individuals buy into the idea that they don't need to change the oil more than every 5 to 6000 miles. (I don't buy a car from a dealer that tells me that, and the guys that I buy from just shake their heads at the thought.) People are people then and now, and I suspect that many, perhaps the majority of firearms of the time got relatively little care in comparison to the ones we cherish and carefully play with today. On the other hand, there were certainly others that were purchased, and stuffed in drawers, under counters, and so forth, and those are the ones we so desperately hope to find at yard sales etc.
I suspect that a large percentage of guns probably DID look like the ones that are "aged" or "distressed" that are available today, and I doubt that it took them long to get there. Reasonable care might well have kept them from rusting (patina) but the bluing and case hardening probably didn't last long in terms of complete coverage on many of them.
Well, this was a long ramble but the question peaked my interest, and you're welcome to your opinion as well - I'll even grant that you might be "righter" than me! Just interested speculation.
Jamie