Does a God exist?

[GrandizerII]

Steve, why appeal to scholarly work anyway? It's not like your views regarding the history of the early church are in line with the mainstream scholarly view anyway.

Now it's likely, as far as mainstream scholarly views go, that there were no intentional fabrication of significant events. But it's clear through analysis of the texts that certain events (such as the nativity events) were added later on to indeed support later orthodoxy. This does not imply fabrication, however, in the deliberate sense. More that later authors (e.g., "Matthew" and "Luke") heard about some additional stories about Jesus, and without verifying it for themselves in a proper skeptical manner, included them in their texts.

As to the nativity, I think that you are neglecting a couple options, that Mark may have been aware, but simply chose not to include it in his Gospel.  Or it is possible that Mark was not aware, but the Matthew and Luke where made aware by their sources.  In his book "Cold Case Christianity" by J. Warner Wallace; he points out that witnesses often do not always provide the same details (some may focus on one thing, that others do not).  Likewise a witness (especially one who is aware of others testimony) may not provide all the details, that they think your already know and rather focus on what they can add.

Except the argument about witnesses providing different factual details due to different perspectives and backgrounds is irrelevant here, because the differences in the nativity stories aren't due to those factors. If that was the case, the proportion of similarities in the elements of the nativity stories should've still been much higher, and the contradictions wouldn't be so apparent. But what we see instead is that the nativity stories were written exactly as if "Matthew" and "Luke" weren't aware of each other's writings. The similarities we do see are those to do with later key doctrines regarding the birth of Jesus: such being born of virgin and being born in Bethlehem. But the nativity stories are just considerably different from each other in most elements.

As for "Mark", most likely when that was written, the whole idea of Jesus being born in Bethlehem and of a virgin had not yet been popularized if at all  surfaced at the time. This specific lack of details about Jesus' birth is also noticed in the writings of Paul. Something like the virgin birth of Jesus should've been mentioned by Paul in at least one of his epistles, but it's nowhere there.