I heard this great piece on NPR this morning about how A Charlie Brown Christmas almost never made it on the air for the first time in 1965. CBS thought that the jazz didn't mix well with traditional carols, that the voices should be provided by professional child actors, and that the tone and themes were too heavy for kids. It turned out that half of the people watching television across the country that night tuned in to watch.
The composer of the soundtrack, Vince Guaraldi, died unexpectedly of a heart attack in 1976. "He was found in a room at the Red Cottage Inn hotel, relaxing between sets at Butterfield's nightclub in Menlo Park, California. Guaraldi had just finished recording the soundtrack for It's Arbor Day, Charlie Brown earlier that afternoon."
He wasn't around to discover that his music had become modern Christmas classics. A remastered edition of the soundtrack, which has never been out of print, has been released this year.