This is a consequence of assimilation and/or integration which follows conquest that does not eradicate the vanquished.
There is study of the Cheyenne tribe from Grinnell, Curtis, Liberty, and I link some of the online Grinnell work catalog.hathitrust.org/Record/000559995 Full view V2 of The Cheyenne Indians (p48) and a list of other stuff he did. There is work by other early 20th Century historians. I have looked at it long time ago and you are correct that no records of membership exist other than passing comment in interviews. Is what it is.
The are political aspects to the history of the battle and the fight for status, recognition, rights and freedoms and a history of survival and aggression. What there was not was a written language and I suggest that men reporting to Agencies for rations might be just slightly wary of registering their membership of war parties.
As per above re 'How many Dog Soldiers were there for the battle?' and if someone is able to do it, the record only scratches the surface because one thing which stands out clearly is that many of them died violently before their time and passed on little. Such a project would find itself barking at a tree. Probably willow.
Marquis's book is far more interesting than its battle content.
Last Edit: Dec 19, 2018 14:34:27 GMT -5 by herosrest
If it walks like a duck, sounds like a duck, and looks like a duck ~ it is probably a goose.