Is it still believed that the history of the Olympics was preserved perfectly? Or is there reason to believe that many of the details were invented centuries later?
I'm not asking about the divine origins of the games. Rather, what I want to know is, is such a list as this to be taken seriously? https://en.wikipedia.org/wiki/List_of_ancient_Olympic_victors
This is kind of a point of contention among historians, but the commonly known "historical" estimate is indeed 776 BCE. According to a Roman historian named Varro, writing from the first century BCE, anything before 776 BCE was an "Age of Fable", the mythical undergrowth of the Olympics where any events described were done so with... quite a lot of exaggeration. Some people think Olympic-like chariot-racing contests began in Olympia as early at the 800's BCE, only forming itself into the four year activity we know and love by the commonly accepted 776 BCE estimate. The first Olympiad only had one event; the one way sprint. Chariot-racing formally began only by 680 BCE, and it only began to grow in size after that. Some people think 776 wasn't the exact date where myth meets reality; an excavator at Olympia swore that the games only began around 704 BCE. Still, we do know that the 8th century BCE brought a lot of Hellenic people together for the Olympics, whether it really started earlier or later in the century.
Source: Spivey, Nigel Jonathan. The Ancient Olympics. Oxford: Oxford UP, 2004. Print.