Thank you, PoppaGator and van lingle. You've said the secret words: thumb-over chords and Wayne Henderson.
A couple of years ago I learned a fingerpicking tune from Wayne ("Victory Rag") that entails thumb-over chords (at least the way I've been playing it). I play it a lot and I've been playing other thumb-over tunes lately, too. That's the problem and that's why it hadn't shown up in the previous 40 years. Ha! Of course, I still have it...