Did you read the article at the link I posted where Bart Ehrman deals with the question of Nazareth? Even if the claim about Nazareth was true it wouldn't matter. It would just be another historical error regarding the Jesus of history.
We know that there was a community of followers of a dead teacher from an early period. They had oral traditions about him long before these were written down. The gospels were also based on earlier written sources.
There is clearly an evolution of Christology within the gospels. Mark doesn't even mention the birth narratives and leaves his audience hanging regarding the resurrection.
Nobody can be certain about which historical details are based on fact and which are exaggeration and which are pure fiction, but exactly the same can be said about almost every character of history.