I wondered about that. The lack of sharpness about the photo makes him look a lot younger than the man in Barry's photos of Long Feather (from 1886?) and, as you say, the other men are from a different agency.
Some of these Kellys are on www.facebook.com/NNAIOP/photos/ They're identified as Miniconjou and the date given is circa 1908. There are several outdoor shots in the same group and I wonder if they are by Kelly too.
Unidentified man with prosthetic leg
This is interesting because the backdrop matches the one in the earlier photos, including Kelly's photo of Spotted Eagle, so I'm assuming the date is early-mid 1880s for this one
John Blue Cloud and son, Green Grass community, Cheyenne River
Last Edit: Jan 3, 2020 10:23:12 GMT -5 by grahamew