@deletethis abject apologies. I did so many things wrong here that a concise explanation won't be possible.
I had chosen e.g Black Day and Dawn from the coop tab of the client Play page, in order to download the maps. In my earlier post in this thread, I referred to those as "regular"; likely yet another mistake.
As I try to re-trace my steps, it becomes apparent that a) I'm still not following the directions in your linked thread, and/or b) there are problems with my setup, resulting in my inability to save. I'll pursue that elsewhere.
In my earlier (6 weeks ago) struggle to resolve my issues, I found those old threads. Not finding a thread on the forum specifically saying it was fixed, I ASSumed it was still broken. (No, I didn't review subsequent patch release notes.)
So, a) I thought that what the OP was attempting to do was similar to what I was failing to do, and b) I thought it was still broken. Apologies for the additional hot air, but you did say "why".