The Gods, any of them, didn't write it. If Yahweh or Elohim did, they sure are confused. Much of Genesis was written by Sumerians, and Eden, etc, was written by the followers the God of light, knowledge, good, and truth: Satan, in a religion that was old when the pyramids were new. You see how this works?
A monk 'calculated' the 8000 date. You refer to this number as an absolute truth, yet don't know the source?
There were 2 Johns, btw. John the Younger wrote Revelations.
No one is sure who wrote the Gospels, they were merely ascribed to various apostles. We know the Book of Matthew, for example, was not written by him, since he describes the Roman census taken when Jesus was born. Such a census did not begin till a century after, with Jesus and Matt long dead.
If no date needed, why are you wasting our time on this?