Well, since there aren't any eastern Bison left around to stufy, I guess its a mute point.
Its ahrd to believe that a bison population adapted ot living in the eastern part of the U.S. didn't exhibit at least subspecific differences from the plains animal - that's a pretty big range for the same species.
The eastern wolf and cougar are recognized as different subspecies from the western animal I believe.
I took an archaeology class about American Indians. It was a intro class that touched on everything from paleo to modern, anywhere from the Rio Grande north. As an off the cuff comment the prof said that Bison bones are common in Plains Indian middens but aren't found in Woodland Indian middens. It's next to impossible to believe the native Woodland cultures wouldn't have Bison on the menu.
Bison did have a wide range and I'm not sure of the details but it's believed that at one time they were two different species that hybridized into the current single species. I know more about wolves and you are correct, there are several different subspecies of Canis lupus. Wolves are generally anti-social to stranger wolves so it's easy to imagine that as a reason for so many subspecies. Perhaps the difference with buffalo is that the herds never became truly segregated. There must have been gene flow across the plains.
A silent one? That kind of works, since there's no one around to say.