I was a DJ in the 70's and we would play a song or two an hour beginning the Friday after Thanksgiving. The closer we got to Christmas, the heavier the Christmas themed songs grew in number in the rotation. But we never went 100% Christmas until Christmas Eve. The wall to wall Christmas music would continue overnight and through about noon Christmas day. After noon, the music began to transition back to the regular format and would diminish over the next few days. Most songs played after Christmas were more holiday music centered than Christmas. No Santa tunes. No Away in a Manger. Songs like Sleigh Ride and Most Wonderful Time of the Year.
The other “oddity” is artists who would have little chance to make the airwaves today are front and center. Bing Crosby, Jimmy Durante, Andy Williams, Burl Ives and others get a great deal of air time on stations that would turn their noses up at them any other time of the year.