All, I recommend Stephen Jay Gould's book on The Millennium, where he discusses lots of this stuff. I can't recall the entire title, but it has the millenium in it. He points out things like the birthdate of some president or other being in totally different months depending on what year you went to grade school, and suchlike confusions. Plus he's so, well, readable...

And don't some $mas carols say that Christ was born "on the 6th day of January" (Jean Ritchie, etc)?