I figured out most of this after realizing that the plugins etc. that I had installed on this archicaduser site were most likely all out of date; I deactivated and deleted them one by one, then uploaded, activated and licensed the new versions. So now I have everything up to date on that site, with a Licenses section that shows the plugins that I’ve installed, and corresponding notices about valid licenses that will receive updates.
One small suggestion: note the current/latest version number of all of your plugins somewhere on your site or in the license section of the user profile, so that one can see if a site is up to date. I know that the admin auto-update should show this info, but in my case (with old plugins) it showed the old version numbers, but no indication that they were out of date.
I’m going to close this ticket, as I don’t need further assistance with licensing and updating at this time.