The Christmas tape is a 100% known landscape. We let hits die but Christmas music is eternal.
That said, there is lots of Christmas pop that doesn't make it into the canon. I have no recollection at all of the first song on the Christmas tape, and i was around then (and going to K-Mart with my mom).
The pop music they use on these tapes are cheap to license --- they weren't even popular when they were contemporary. They were just generic cheap music.
For Christmas, there is a set of Christmas music that just gets played every year and is licensed in blocks that are fairly cheap. That's why you hear a lot of "traditional standards" and not much else.