Thank you Zak! This was very helpful!
Confirming that the two ways of specifying library paths are the same, with the only difference being manual vs monitored, means that things were in fact working as they seemed to. I prefer to scan manually as needed, but wasn't sure if the way I was doing it had the same results as setting it up in preferences. I can see how the two could work together in useful ways.
Maybe I've misunderstood what you're doing, but if "the path had been removed from the list in the File -> Scan window", how will MusicBee know if any files in that folder have been deleted or moved?
Even if there are no new files, you would still need to include that folder to avoid having entries in your Library for files that no longer exist.
I didn't explain what I'm doing too clearly. Your questions in response were clarifying. Cool!
So using the File-Scan window, with a given set of paths, when I moved items from one place to another within that set, and then ran the scan, MB would list the files that were not in their expected location and ask if they should be removed from the library, and I would say yes. At the same time, those files would appear in the library at their new location. That all made sense.
What I also found, or think I found, is that if I remove a previously scanned path from MB's list, and then rescan, MB does not report any missing or misplaced files, or pathless files, and the files that were added from that path remain in the library as before. That was somewhat unexpected.
That then led me to realize that files can be in a playlist but not be in the library, if they are dragged directly into the playlist from Explorer. To get them into the library (and searchable by MB) they need to be added using the send to library command. So playlists can be used like the inbox in that way.
All very interesting...........