I'll leave this up for a while, giving people who have any interest, a little time to think about it, then I'll describe and post scans, of the test results. I alluded to it in last night's thread regarding the Horner Wagner, but now the test subjects are 'stable', so I can scan them.
Edited: I'm not going to bump this thread, but here are my thoughts on what this item is.
I believe that it is either a prototype of some sort, or it's what Nash hypothesized, but I lean toward the former - Williamson was a professional and would not have distributed something of this quality as a final product: the image does not match the mount, and the mount is re-used. These are actually facts that you would have to be blind not to see.
It could be a prototype for something similar to the 'ticket photo' of Wright, that's coming up in REA's auction. As such, it could have been presented to a representative of the Atlantics (at their request after a team photo sitting, or on Williamson's initiative), the possibilities for use described to the representative, and then the idea fizzled. The loc item, also 1-of-a-kind might be another 'prototype' item that was created by Williamson at the same time. In other words, he was experimenting. There is another possibility, based on the fact that the two images work together as stereoview components, that I won't address yet.
Yes, other than the fact that it's poorly constructed, it looks like a normal carte-de-visite. But it does feature a baseball team, and hobbyists are well aware that many (most?) such items (team baseball cdv's) were actually used as advertising, as opposed to the cabinet and imperial-size team photos that were distributed to team members. Size is key here.
That's it for now. I have at least two additional tests to run, but I have decided to limit their distribution to a very short list of interested email recipients. Everyone else can put their blinders back on.