FINALLY! It occurred to me to try this:

[root@seveneves ups]# journalctl -u nut-driver@seveneves-ups
Apr 27 09:16:34 seveneves.gregandeva.net systemd[1]: Starting nut-driver@seveneves-ups.service - Network UPS Tools - device driver for NUT device 'seveneves-ups'...
Apr 27 09:16:34 seveneves.gregandeva.net nut-driver@seveneves-ups[466866]: Network UPS Tools - Generic HID driver 0.47 (2.8.0)
Apr 27 09:16:34 seveneves.gregandeva.net nut-driver@seveneves-ups[466866]: USB communication driver (libusb 1.0) 0.43
Apr 27 09:16:34 seveneves.gregandeva.net nut-driver@seveneves-ups[466866]: Fatal error: 'maxretry' is not a valid variable name for this driver.

So it seems that an edit to ups.conf was also needed. Commenting out the maxtry line (which has been there literally for years) gets things working again. Thanks again to Robert and Jeff for pointing me in the right direction.

--Greg