Thank you for the reply.
While its may seem strange, some Mac people have been complaining about lost files in Music (Reddit, MacRumours). I keep my folders in Media rather well-named and organized, Apple having taken every keystroke mistakenly added to artists entered as a different folder. I also change some titles and details about the music often (I'm a collector of regional Eastern European music, and I'm learning a lot about classifications, which I enter into Music), so I may be confusing the poor app. Still, having music disappear is what has happened, even though every test of my hard drive shows no problem. Other files have not vanished from the drive.
Nonetheless, I have rebuilt my music database from backups to another drive, and was successful in gaining all but 100 or so pieces of music lost. I'm tracking when Music fails to locate a number, and already since the rebuild it has "Lost" two. I do not have a large database (11,000, with no purchases from the store), so it shouldn't be size that causes this.
As to other apps, I've found they either work off of Music's collection of playlists, or do not allow the detailed information entry I require, so I'm using Fidelia for better quality sound, but entering music that needs it (classical, etc.). I'll be watching the drive to see what happens in the future.
Again, thank you for the reply. I rely on those who have a deeper understanding of how apps work in the background, as I'm too old to fuss that much!