If Joseph's fear of taking Jesus into Archelaus' Judea didn't abate until the Herodian Ethnarch was exiled in mid-6 AD, then Matthew 2:22 would explain Luke 2:42, meaning that Jesus' twelfth birthday fell somewhere within the twelve months before Passover of 7 AD. In turn, this means Jesus was most likely born between April of 7 BC and March of 6 BC - a timespan which has a lot else to recommend it as the proper window within which to date Jesus' birth.
I've said this before. I just felt like saying it again.
If anyone wants to investigate further, and publish something along these lines, I'd love to collaborate. I'll also happily settle for a footnote. Just read the rest, please.