I forgot about Part 97, Sec. 97.21 (a) (3) (ii)!!
In reciting the various statutes and regulations which provide for the day-to-day renewal of an amateur license when the renewal application is timely filed but not routinely granted, I forgot to mention that the same provision is contained in Part 97 itself: Sec. 97.21 (a) (3) (ii). I remembered this only after reading a post by N5IMS on this forum. Thank you, N5IMS. You seem like a smart guy, and I'll bet we could have interesting discussions of amateur radio legal issues.