Well, it was probably wide open only for me. And I finally sort of understand what is going on ... maybe. I think this is what was going on:
I told Windows to remember the credentials I used when accessing the share MyBookLive\Secure. Windows saved those credentials (in my AppData) under MyBookLive. Then any time I (but nobody else on the PC) tried to access MyBookLive by name Windows (but not MBL) demanded those credentials, and since they were saved, Windows automatically provided the credentials when I (but nobody else on the PC) accessed MyBookLive\Secure.
My intent, too, was to provide a share safe from ransomware, but that did not happen since the "secured" share was open for me all the time.
Now I've messed things around enough that I can't access the secured shares at all, but I can access the public shares without providing credentials.