Richard Owlett composed on 2016-09-10 09:50 (UTC-0500):
Made multiple further tries installing various packages. Got
inconsistent results. The pattern leads me to believe the drive
is becoming flaky. I will create an ISO from the DVD for use on a
flash drive. 50+ years of trouble shooting in diverse
environments is educational ;/
Flaky SATA behavior could be a bad cable. Is your DVD drive
connected via a red cable? If so, try replacing it.
https://lists.debian.org/debian-user/2016/02/msg00321.html
https://lists.debian.org/debian-user/2016/02/msg00372.html
http://permalink.gmane.org/gmane.linux.ide/54404