On the American Top Forty from June 29, 1974, Casey Kasem introduced the latest hit from ZZ Top, a little song called "La Grange," entering the countdown at Number 33. There's only one problem with that: "La Grange" never even reached the Top Forty, peaking at Number 41.
How did this happen? Well, Casey had been invited to appear as a guest star on Hawaii Five-O, which necessitated his being away from the AT40 studios for a few weeks in the summer of 1974. They had a special countdown teed up for the Fourth of July weekend, "Top 40 Acts of the 1970s, So Far," but they tried to cheat the first week by guessing at how the Top Forty would fall that week and recording a show based on those estimates. They got the Number One song right, Gordon Lightfoot's "Sundown," but according to my sources, they ended up with only three songs in exactly the right position.
And Casey inadvertently gave ZZ Top their first Top Forty hit. In actuality, the Top wouldn't make the countdown until 1975's "Tush," which went to Number 20.