Some Christmas Carols are not Christmas Carol so those are safe. Haha Carol of the Bells is an Ukrainian traditional song about wishes of abundance that has nothing to do Christmas except for the fact they borrow the music and added a Christmas lyric but the original words are absolutely different. Same happens with whose child is this? which is actually the Elizabethan greensleeves ballad. So you can always trace back the original words and non xmas version lol. Some are indeed super interesting pieces of folk music