[Snowman]

This is a fascinating discussion. I'll start out by saying I know nothing at all about Civil War era photography or stereoviews. But I do have two comments to add that I think supports both arguments.

1. Male pattern baldness comes in several different forms, but the form in which an individual experiences it is determined by their genetics. One can't switch between types of male pattern baldness, they can only continue to lose hair that is consistent with their type. The man with the eyebags (I believe you identified him as Duncan Curry?) appears to have two different types of male pattern baldness in the two photos. Perhaps the younger photo is a combover of sorts? Perhaps they're not the same person? I don't know.

2. Probability theory informs us that the probability of the group photo being the Knickerbockers based on the individual probabilities associated with facial recognition algorithms of each individual is proportional to the product sum of those probabilities. In other words, if the probability of each person being a "match" is 90%, then the probability of the group being the Knickerbockers is equivalent to the 1 - (0.1^6) = 0.999999 or 99.9999% chance that this is the Knickerbockers. However, this is based on the assumption that a "90% match" actually means the individuals in two photos are 90% likely to be the same person. I don't know if this assumption holds true, and wouldn't be surprised at all if it didn't. I don't know enough about facial recognition software to make that claim. But I do know enough about probability theory to know that if all 6 are high matches then the group as a whole is a MUCH MUCH MUCH higher likelihood of being a match as well.