Ok, how about approaching this from the other direction.
How old were you last year and what year were you born in?
For me, I was 34, and born in '76. So that adds to 110.
How about in 2001? I was 25 and born in '76. That adds to 101.
So it doesn't have anything to do with the date... it's just however old you are, and adding that you your birth year.
Then somebody clever comes along and picks out dates that "mysteriously" correspond to that number.
So in 2001, everyone would have been mystified to find 01/01/01, or 10/1/01, or 10/11/01, just happens to add up to our age+birth year.
It doesn't work every year, because in some years, our age+ birth year adds up to some number that doesn't make sense on the calendar. :)