The following post was from February 2010. Due to the large amount of questions regarding this issue, I thought a repost was warranted.
Understanding Andy Warhol's 1986 "Cowboys and Indians" Portfolio is confusing. Twice this month I've had customers confused about the Sitting Bull. Well, it is confusing! There is even more confusion surrounding "John Wayne" but that is for a later blog!
Each of the 250 Regular Edition Cowboys and Indians Portfolios contain 10 different prints:
Geronimo
Mother and Child
John Wayne
Plains Indian Shield
Custer
Annie Oakley
Kachina Dolls
Indian Head Nickel
Northwest Coast Mask
Teddy Roosevelt

John Wayne (regular edition)
Each of the unique 36 Trial Proof Edition Cowboys and Indians Portfolios have the above listed 10 plus 4 more for a total of 14 prints. Each print has a unique color combination.
Sitting Bull
Buffalo Head Nickel
War Bonnet Indian
Action Picture

Buffalo Head NIckel (trial proof)
To add to the confusion, an unknown number of like-colored Sitting Bulls were printed for the Regular Edition but not used. It's thought that they were to be one of the 10 in the Regular Edition but were replaced by another image at publication. These are available on the market and are not signed or numbered. These Unpublished Sitting Bulls have been authenticated by the Andy Warhol Art Authentication Board and Estate of Andy Warhol.

Sitting Bull (unpublished)