This is almost certainly a case of a current collector wanting a Pinkerton-style cabinet of Wagner, and simply gluing a trimmed Bain photo to the nicest dark grey mount he could find.
Basically, if you plan on keeping it and you like it, then it doesn't matter. Otherwise, you are going to have a tough time convincing anyone that back in 1909 a photographer in a studio in Canada picked up a photo from Bain, trimmed Bain's name from the bottom of it, and then glued it to his own mount, with his own studio's name printed on the mount. While some here may think that was commonly done, it wasn't.
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