1557:
Photocopies of Colt letters are always suspect, because they can easily be altered. If the revolver was custom made it wouldn't have likely been included in a 30-gun shipment to a distributor. Also given the name, I think that Colt's historian would have commented much more then she did if they could connect this particular gun to a genuine Masterson order.
Masterson ordered a number of guns from Colt, many that were nickel plated, and some that had ivory stocks. These particular guns are known, and have been cited in better research books on Colt Single Actions and/or western history.
During the early months of 1882 He was in or around Pueblo and Trinidad, Colo. Yes, while there he did order a gun from Colt. Yes it did have ivory stocks. But Masterson ordered that it be sent directly to him, and as quickly as possible. Letters from Colt to Masterson confirm that they did so. To further confuse the issue, Masterson also ordered guns for friends.
All of this information is, and would be available to someone creating a fake. I'm not saying that happened, but when dealing with guns that supposedly belonged to a famous person and carry a multi-thousand price tag one should be particularly careful.