No mystery here. There were a number of Crow scouts who came on the scene shortly afterwards and found Custer’s body at the ford. One scout’s widow told the whole story to Frank LIndemann a/k/a “Signtalker” (because he was fluent in plains sign language). Book is still in print, “Pretty-shield - Medicine woman”
The Crow scouts never found Custer's body at the ford (by this I take it you mean Medicine Tail Coulee). The Crow scouts fought with Reno then left the battlefield. Curly was with Custer but never made it to the ford or Custer's area of battle. He did view it from a distance, but his testimony has changed over time.
Custer's body was found on Custer Hill by the soldiers under Gen. Alfred Terry once they arrived at the battlefield. The present marker is an approximation of where the body was found.