The main difference is that the US Army had payroll records and the Indians didn't.

The army had estimates of Indian casualties, some based upon observed burials, and others not.

If there is an event in the history of the United States where the foibles, weaknesses, and follies of historical research are revealed better than the Little Bighorn it is a matter of dispute.

Historical research is a great pleasure and requires a degree of rigor. We will never get it right, but we can try.

I recommend all  read Carol Reardon's 'Pickett's Charge in History & Memory,' Chapple Hill, 1997, University of North Carolina Press, ISBN 0-8078-2379-1.

"Frustration will likely remain the lot of the purists. As a disgruntled veteran noted in 1913, "Pickett's charge has been so grossly exaggerated and misrepresented as to give some color to the oft-repeated axiom that 'history is only an agreed-upon lie." This, the second to last sentence in her book, cited "Pickett's Charge," National Tribuen, January 29, 1914.

Dig on ladies and gentlemen, we might refine the agreed-upon lie.