i would argue that the more time and the more times the story has been copied and retold the more likely it is to be modified to suit someone's agenda.

the only way to eliminate this is to cross-reference it with contemporary texts that they agree on points. and this can also be a problem, because those who would manipulate "holy books" for political ends are probably also burning books.

the naivete of so many sects of the "people of the book" in its various flavours in it being "the word of god" is a totally disingenous expression and an entirely arguable point that should not form the foundation of faith.