Final answer:
The original Choukoutien human bones were lost during WWII, not Kennewick Man's. The Iroquois Confederacy didn't maintain complete neutrality during the Revolutionary War. Sources about Quetzalcoatl are primarily post-conquest accounts.
Step-by-step explanation:
The original Choukoutien human bones, often associated with Peking Man, were indeed lost during World War II when Japanese forces occupied China. However, the question seems to be malformed or based on incorrect premises. The most famous human remains discovered on the American continent over 9,000 years ago were found in Oregon and are known as the Kennewick Man. This has led to a legal and cultural debate over the repatriation and study of such remains between scientists and indigenous groups. The case mentioned is akin to this scenario with the Kennewick Man rather than the Choukoutien remains. In terms of the Iroquois Confederacy during the Revolutionary War, it is false that all tribes maintained neutrality. Different tribes within the Confederacy chose different sides in the conflict.
Regarding the myth of Quetzalcoatl, sources about Quetzalcoatl as they relate to the conquest of the Aztec, it's important to note that most of the written sources referenced are post-conquest accounts compiled by Spanish chronicles and priests. Many of these accounts had particular agendas and should not be considered as contemporaneous with the actual events of the conquest.