Griffon,
This is a suggestion that might help you or not as you might have already done so. Google "Winchester 1 of 1000 pics". It's pretty obvious the difference between an original and the ones that we're faked! IMO! Even the trim at the end of the barrel band was platinum in most cases which has a duller appearance than the replicated gold look. Even the Turnbull restorations are great examples of the original models. IMO! In 1950 Steve Hannagan of N.Y. did a report on these Rifles that's pretty interesting. In "The Hannagan Report" he talked about such Fakery involving these highly sought after Rifles that Winchester claimed to shoot better than most in their production whether a model 1873 or 1876, and a "one of 100" or a "1 of 1000". In 2009 Edmund E. Lewis MD. came out with a very detailed book that has a large amount of the most up to date information on these Rifles. Like was posted by Pocanojack Pics. would be help full, besides, we'd all like to see it! I'm also wondering what the Serial number is? If you want you can PM me and I'll look in the serial records I have for the known ones and verify in case you don't want to put it out there.(understandable)
The 1 of 1000’s were engraved not stamped
Pics would be helpful
He's also correct on the engraving!
As far as your question on the counterfeit stamp and it affecting the value?
Well that's the Golden question naturally! Remember there's a buyer for everything and you just never know!
Without more info. and pics. I think that question is as big a mystery as possibly the Rifle!
HS 58