That's the thing, I did all this research and didn't find where that one charted. And as mentioned before, yes it is the most-played song from "The wall" on radio, next to Brick-2. But I was too young to actually remember 1979/80, so when I say it's the most played I mean on classic rock radio. BUT I did find where a medly of Brick2/Don't Leave Me Now and some others charted on the Club Play Chart in 1980. Yeah surprised me too.
Lumiere mentioned that "Free Four" and Stay were played in America and finally got Floyd some airplay over here (or "there" depending where you're at) and that's right, but unfortunately it didn't actually chart.
Maybe the thing with CN was like an album-rock situation where album tracks from the album get played but don't necessarily chart as singles.
And Lumiere don't worry I wasn't putting the tracks from the albums in the order they were released.