It was a lot harder to hear the "Chain" connection in the "Butter Cookie" they used in 2005 (the one that sounds like the Bob Welch era) than in this latter one from the most recent reissue. The chord progression of the chorus is right there in it, as is the whole coda.
And then there's the following, which is the "Chain" verses being worked out lyrically and musically. The chords and picking style of the final verses obviously came from Lindsey.
The Chain Writing 02
The Chain Writing 03
Given all the pieces we have from all three writers, I think it's safe to say that we have a very clear picture of how that song was concocted. It used to be a major mystery, but it is no longer.