So here’s what we know from the legends (that we can probably accept now that we, as readers and viewers, know they are very real and very dangerous): The Long Night took place during a winter that is said to have lasted an entire generation, killing kings in their castles and bringing a cold that has never been seen before or since. It’s why the kingdoms ignore the alarms of White Walkers to fight over an Iron Throne too bad all of that bickering will mean nothing if The Long Night descends upon the Realm again. Yet to most of mankind the White Walkers are a myth: something people rarely believe existed, or lived so long ago they are gone from the Realm-like the Children of the Forest ( oops). The Long Night is a curious piece of history in that we know more about it right now than anyone that lived in Westeros for 8,000 years. Except in Westeros circa 8,000 BC, the most important battle of all-time took place during an event known as The Long Night, when White Walkers (in the books known as the Others) almost ended the realm of the living.
This would be like someone writing about the life of Julius Caesar for the first time-ever-today.
So of course anything that took place in 8,000 BC wasn’t written down for 2,000 years.