This is especially true in the case of supreme rulers who failed in some way. History is littered with rulers who erase and re-write history to cover their failures.
One can well imagine that, had the American war of independance begun in 1776 B.C. instead of A.D. the story would have transmogrified considerably as it passed from generation to generation in a less than scientific era.
Not necessarily. If it was written down at the time, and copied faithfully over the centuries, it would still be as accurate as the day it was recorded. Even stories passed down orally can remain accurate for many generations. My grandfather told my dad and I about an ancestor of ours who was wounded fighting against the British during the American Revolution. He heard the story from his grandfather, but could not remember the name of the ancestor. He urged us to try to find the ancestor's name by searching the Revolutionary war pension records at the National Archives. We found the battle story, and it was exactly as my grandfather had told us. In this case, the story remained accurate from the 1790's until the 1990's. There was some information *loss*, (the name) in the verbal account, but no corruption of the transferred information.