Coastal, thanks for the tip, because that's where the problem seems to have been centered.
I opened CCC and (never having even bothered to check for this before) checked the "snapshot" pane. Sure enough, there was the item that I had been looking for -- with the date that was the same as the one revealed in terminal (from my post 34 above).
Well, CCC's documentation said you could delete it by right-clicking and choosing delete.
I tried that, and CCC threw back an error msg saying the deletion didn't work and I should try restarting the Mac.
I restarted, tried again -- with the same results.
I then tried going to CCC's menu and choosing "uninstall CCC" (hold down option key while clicking on "CCC" in the menu bar). The uninstall dialog gave me the option of also removing any snapshots. So... gave that a go.
I then re-opened CCC (for some reason, when you "uninstall" CCC using the menu choice, it leaves the CCC app in your applications folder).
The snapshot was STILL THERE.
And again, it couldn't be deleted.
Something, somewhere, was corrupted.
So...
I did it "the Fishrrman way":
- Booted from an external boot drive
- Did a "get info" on my internal drive, and checked the option to "ignore ownership on this volume" (makes it easier to nuke stuff)
- Launched "EasyFind"
- Put "bombich" into the search string and let it go
- There were about a dozen hits, I deleted them all
- Then went to the applications folder (on the internal drive) and manually deleted the CCC app.
Next, I rebooted back to the internal drive (2018 Mini).
I then downloaded a completely fresh version of CCC.
Opened it, went to the snapshot pane.
Right clicked and chose "delete"...
... and finally, it deleted and was gone!
This reclaimed about 10gb of space on my boot partition, which is 150gb in size.
So 10gb makes a difference.
But that took some work (and the time to finally figure out what to do) !!