CHRISTMAS SONGS along with “Auld Lang Syne” are the only songs we hear and sing once a year. Hoping to write about the most popular carols, I discovered songs I had never heard of on the many lists of Most Popular Christmas Songs. Even when I listened to them on YouTube, they were unfamiliar. Can you sing a verse of “Purple Snowflakes” or “Ain’t No Chimneys in the Projects?” Songs by Justin…