Not to nitpick, but Grimes did not record between 12/18/66 and 2/9/03 (according to Mike's discography), so we're talking more like a 36+ year absence, at least on tape. I wonder when his last known gig was before 'retiring', and when his first comeback gig was. That will tell us exactly how long he was out. I suspect it's at least 30 years.
It's amazing how great he sounded after such a long hiatus. I wonder if anyone else in jazz has been away that long. I'm thinking of Terri Thornton, although I don't really know that much about her chronology.
Bertrand.