Missing?
Probably nothing
The whole virgin birth debacle starts in the old testament with the original prohecy and the mistranslation between "almah", "young woman" not virgin. and "bethulah", meaning "virgin" which probably gives Hebrew scholars a laugh when they look at some Christian texts. Virgin births? Vishnu, (sorry don't remember the goddess) and Isis in the Egyptian (yes I'm stretching a point there with virgin as it was self impregnation, using the ancient equivalent of the turkey baster
).
As the language in use in the Palestine area was Aramaic, why would the original text be in Greek? Greek came into use with converts when the message was brought to gentiles, but Virgin births also formed part of the hellenistic tradition -hmmm when did it appear in christian belief? The earliest texts available, hard one as you say. There was a story about some relevant texts being found with the dead sea scrolls, (circa 1977) this seems to have been either totally false or covered up as I have not heard any more about it, perhaps in more scholarly circles? (The translation of the dead sea scrolls is also another can of worms which could be the subject of another documentary
)
You are obviously a Christian and a much better biblical scholar than me, I hope I have not given offence as I am an agnostic and do not take religion very seriously, I do hope however, that I have offered a little food for thought.