On 70s on 7, Thursday's "Wheel of Casey" (an American Top 40 episode that can be from any week, any day of the 1970s) featured a countdown but no show. The open ran, announcing a date in March 1971, then the automation went into "We Got To Get You A Woman", then a few more songs from 1970. As I've mentioned, there are folks who follow and tweet along to the countdowns on Twitter. An astute tweeter figured out the countdown was from December 26, 1970 but only the songs, no liners, no promos, etc. It seemed as the songs for a countdown were entered in to keep music rules, artist separation etc but the actual show didn't fire, and of course, no one home to realize it. I don't know if the year-end episodes started the first year of American Top 40.