The joys of Catholic school, I know all this crap...when it's rammed down your throat for 12+ years, it gets old and you tend to hate it. Really, the bible's been written, re-written and by so many people, things are left out, and most of the Gospels were written years after the things happened, so a lot was forgotten. Heck, Judas wrote a Gospel, IIRC, as did many major characters in that time period. Theology was an easy A, and a required class.
Their main point was not to be exact, but to give a general idea and message.
If you're going from the date of the Annunciation, it does coencide with Christmas. But they're just dates.