1. I'm not sure what could be wrong with the files. Each folder on the PC was created by reading the CD tracks with Sound Forge and placing them into a named folder. Each file in the folder is named also (by me, as Sound Forge only uses generic names). Everything I am trying to bring into the library was created using this exact method.
2. However, I think you have put me onto the right track. Looking at the Song view, I searched for an item in a folder I had tried to load but which appeared to fail. The songs showed up... added to the last folder that I had loaded. When I looked at songs in that album, it had a random selection of songs from various folders, including all the items that were the correct ones. I deleted that album and then added that folder again. This time the right files came in. However, things are still weird. When I then added the next folder I wanted, the songs from that folder added into the album that I had just previously loaded. More oddities. I selected a completely different folder to add. This time, all the song came in UNDER THE ALBUM NAME of the one I had just deleted. Further, it contained not only those songs, but a random selection of other songs from other folders. So I deleted the album again and picked yet another folder. This time the songs from that folder came in, but under the same album name of the one I had deleted. Very confusing. I renamed the album to the correct name and attempted to add yet another one. This time the songs came in from the one I selected, but again added to this was a random selection of tracks from other folders in the source area. So apparently something is corrupted somewhere, but I am not sure what to do to get back on the right track.
PS: Thank you for your ideas thus far. At least I can see sort of what is happening, although there seems to be no discernible pattern.