I apologize for what will be a disjointed reply to various posts.
The original poster writes, “It's also possible that a previously-taken photo was made into the stereoview by taking a picture of that picture or using the negative process of that era.” There is more assumed in this sentence than is immediately apparent.
To create a stereoview in the middle of the nineteenth century, the photographer needed a camera with two lenses placed as the eyes are, side-by-side. With two lenses, you have two images, each slightly different. One could not take a single photograph, taken with one lens, and turn it into a stereoview. There must have been an intention to take a stereoview.
Your albumen silver print stereoview was taken using the wet plate collodion process. That process was not invented, I believe, until 1851. Prior to that time, photographers like Fox Talbott used paper negatives (when they used negatives at all), which recorded much less information than glass negatives.
I have made wet plate collodion negatives, and printed them on home-made albumen paper, and I have also made ambrotypes and tintypes, all of which are wet-plate processes. I am less knowledgeable about the chronology of the development of these processes, but am confident that if your stereoview was printed later, the original could not date from the 1840s.
As to whether the stereoview was taken or printed by the Anthony brothers, there is no evidence presented for such an assertion. I believe Henry T. Anthony was a member of a group that traded stereoviews, and I vaguely recall that some of these stereoviews survive with notes to fellow members on the verso. If that were the case here, you’d have a more compelling argument. But there is nothing about either the prints or the mount that tie it to the Anthony brothers.
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