On a mind tangent from ^^^that^^^ I thought of this. (don't ask...)
I have a copy of Woodstock, WHOLE 3 hours, I got free from youboob. Years ago. I was watching this song especially. This video just has a picture, but in the movie you can see Richie playing... weirdly. He wraps his thumb way up over the top of the neck, playing 2 or 3 strings with it in a straight bridge. So I knew he had some funky tuning on the guitar. There's one point where he breaks a string onstage and fixes it. When he gets done you can see and hear him tuning it. So I tuned my guit like that and this song just fell into my lap! I knew how to play it before I played a note. Just immediately started playing this!