Um, don't need screenshots. When Finder>Prefs is set to show external disks, all mounted volumes/partitions show up as separate icons. I can tell Spotlight not to index any of these individually, by name. They were created as disk partitions, and are each listed in /Volumes. I will call them partition/volumes.
I use SuperDuper as well, and do scheduled "Daily" and "Weekly" backups on another disk drive box. Each is a separate partition/volume. Two partition/volumes on one drive box. If I wanted Spotlight not to index those, that would be easy! Just tell it not to index the volumes named backup.weekly and backup.daily. BUT, I'm talking about a separate drive box that I manually do monthly backups to. As in, for my 9/1/18 backup, I power up the box, select the old backup.6/1/18 volume, write to it, and then relabel it backup.9/1/18. That way I KNOW when the monthly backup was done, and there are several monthly backups available on that drive/box. This is, as far as I'm concerned, an optimal backup strategy for me. I don't want to argue about optimal backup strategies.
This isn't about Time Machine. I don't use it.
What I want is for Spotlight to NOT grind and grind and grind on indexing my monthly backup when I plug it in and turn it on. That's what it does. If I tell it not to index backup.9/1/18, it will delightedly index backup.10/1/18 the next month. What I'm asking about, and I'm converging on understanding that there is no solution, is somehow telling Spotlight NOT to index "backup.*" (as in, all partition/volumes with a name prefixed by "backup") or, for that matter, any partition/volume on that disk/box. The only way I know how to do it is to turnoff Spotlight entirely, and I'm reluctant to do that for this machine.
I'm sort of explaining myself over and over with the same words, but I'm not sure y'all are understanding what I'm saying.
There is some ambiguity here. I call a box with a motor and a platter a "drive". Many people call a volume a "drive". But in the latter case, you can have many drives in what I call a drive. I want to tell Spotlight to not index anything in a particular box with a motor and a platter.