It's not unheard of to see a photo of a popular subject mounted and sold by a different photographer; I had a Horner photo of a famous bicyclist mounted and sold by another photographer on his mount. I'm sure the same thing happened with other popular subjects, actresses, baseball, etc. Possibly unauthorized copies and sales, but 'legitimate' cabinets from the time.
But you don't see that often, and 1911 seems a little late for that, I associate it more with the "golden age" of cabinets, 1880s, 1890s. Because of that -- and also some things going on with this Wagner photo, like the thin white line at the right edge and the x-acto-sharp corners of the image -- I'd be skeptical that this is real.
Did some looking around -- you can get a giant high-res file of this image from the Library of Congress:
http://www.loc.gov/pictures/item/2008677272/
You can see that the "cabinet card" has less detail, muddier blacks, a flatter tone, and is in general a worse print -- which you might expect with a recent print rather than a vintage silver print. No smoking gun, just my two cents.
David