“When Ryan Booth began his research into Indian scouts who were recruited by the U.S. Army, he discovered only two military forts had complete records of the scouts: Fort Apache in Arizona and Fort Keogh at Miles City.

“Historian collecting stories, artifacts of Northern Cheyenne scouts at Fort Keogh in Miles City”
--Susan Olp
BILLINGS GAZETTE
January 7, 2019
https://billingsgazette.c...43a9f.html

Grinnell provides some details on this – much of it gathered first hand.
George Bird Grinnell. The Fighting Cheyennes (1915 / reprint 1983).

I was interested that only Fort Keogh and Fort Apache had complete records. Maybe because they stayed in army hands longer.