Firepoint, indeed AT40 was designed to keep the music flowing and the music was edited, cut and Casey’s precision was tight. You may note Casey was IN the music vs overpowering it, which for the time was actually fairly revolutionary.
It was believed that since everyone knew the hits being played, the music was second to what Casey was saying and the audience accepted literal snippets of the music in favor of energy and moving toward the number one song “faster.”
That kept listenership higher for the show and over the years.
Additionally, remember there were/are national spots and local spots so maybe Atlanta would have a larger local adv load than say Pittsburg, so each market would have different timing.
Today’s AT40 (on Hippie and nationally) is from 1979. You may also notice an extra from Prince which was literally released two months before this week back in 79 and hit number 11 two months from now before becoming number 1. So that “fill” is a good example of keeping the extras within the time frame, but not yet on the charts.
Notice how the segments are dissected and often the intended breaks become back to back segments without a commercial.
That may sound completely different in various markets and is designed that way.
Now on with the countdown. LOL.