>Somehow these got written down real well.
Thousands of years before writing existed?
It even goes to issues other than writing. Early man understood quantities as 1, 2 and many.
Then came 1-10 (fingers), then the advanced decimal system we now use.
But early Biblical stories refer to the ages people in the high hundreds, many centuries before either writing or numerical understanding existed.
The Bible versions got written down well, as the manuscripts of the bible, silly. If close variants were popping up all over the place, we'd be seeing them appear in, say, cuneiform writings. This requires a paranoia level conspiracy theory to believe.
And look what happens to the ages up to, and following the Flood. There isn't a step function in the ages; it's a plateau up to the Flood then a decay to the values we know today.