Rita Coolidge: Superstar
Joe Cocker: Delta Lady
This explanation will read more like Six Degrees of Separation than a normal musical post. Let's see if I can get us through the maze.
Leon Russell began his career as a 60's session musician and songwriter. Sometime around 1969, he was an integral member of Delaney & Bonnie & Friends, a transient group made up of Delaney and Bonnie Bramlett plus or minus George Harrison, Eric Clapton, Duane Allman, Dave Mason, Booker T. Jones, Isaac Hayes, Bobby Whitlock, Jim Keltner, Rita Coolidge, and a boatload of other musicians. Together Russell and Bonnie wrote "Superstar," an unnoticed B-side single for Delaney and Bonnie in 1969.
In early 1970, Russell went on to produce Joe Cocker's Mad Dogs and Englishmen tour, and he's featured soloing on several tunes on the very successful live album. As was Rita Coolidge, who does a bust-up job on "Superstar". Even so, you are probably most familiar with The Carpenters' 1971 version. Richard Carpenter, though, had heard neither Bonnie's or Rita's version, but instead caught it on a TV show performance by a then-new vocalist, Bette Midler.
Meanwhile, in this fertile period of cross-collaboration, Leon Russell also wrote a song about the aforementioned Coolidge, at the time nicknamed "Delta Lady". Cocker picked up that song and made it a hit in 1969. Leon recorded his own version a year later.