I know not how, but my dynamic archive funk seems to be resolved. In thinking particularly about why (1) new entries would display as expected, but old entries wouldn't and (2) archive mapping had to be changed from original in order to work, I wondered if the backup templates could have anything to do with the problem (causing some kind of conflict? I don't know). Well, I deleted every last one of them (200 or so) and voila! it's all good now.
Wonders never cease.
