Just thinking out loud, so I apologize if there are easy answers to these questions...
Why is the Bozeman Bulger letter on New York Highlanders letterhead? He didn't work for the team, did he?
When was the Bulger letter first discovered, was it known back at the time, or in the decades after, or did it not come to light until more recently?
Given the number of different subjects in the set, there should have been almost 400 of these letters either delivered in person at the ball park or through the mail. Is there a reasonable explanation as to why this is the only one that has been discovered to date? I am operating under the assumption that permission would have to have been granted (based on the 1908 law) for any likeness to be sold, with not only cigarettes, but also gum, candy, bread, etc. That would require many more signed letters of permission across major and minor league players, across many different sets and they would have to be held on file at multiple different firms (American Tobacco, American Lithography, as well as various candy manufacturers, etc.). If it was just American Tobacco (or American Lithography), I guess they could have all been destroyed/thrown away at the same time. How likely is it that all of these signed letters would suffer the same fate across many different companies?
Adding on, based on a quick Google search
The letter was owned at one time by Barry Halper. Weren't there some items that Halper owned that were later discovered to have been forgeries? Is it possible for the envelope and letterhead to be real, but the actual content of the letter to be a fake? By that I mean, the envelope and they letter down to "Dear Neil," as genuine.
Are there any examples of Bulger's signature that can be compared to the letter?
Again, I am just thinking out loud and do not have any ax to grind here, no need to fire arrows at me