Iesou Chresto -

[Confused Ape]

There is an assumption there that it started out "written" at all. These were largely pre-literate societies. Only a relative handful could read or write. The most likely genesis is that these began as stories, 'tall tales' if you would which were eventually written down. Who knows what they were originally.

Scholars only have written texts to go by. It's very likely that stories were eventually written down but we have no idea if there were major alterations in the process of writing them down. It would really depend on the agendas of the men who produced the first written versions.