If you are looking at the original file, then that's probably the problem.
On a Mac, the iTunes preferences are usually set to import the music and manage it, so it copies the files into the Music/iTunes/iTunes Music folder and creates a new folder based on the Artist. There are sub-directories for the Album names. Those are the files that can be managed and changed by iTunes.
Since I only collect full albums, it's no big deal for me to copy that newly created folder (with my meta data changes) onto a backup drive. I delete the original music as it's a waste of space and the meta-data is wrong.
If I don't want to keep the music in iTunes, I remove it by using the iTunes interface. Never remove the music manually from it's storage folder because iTunes is a database type program and won't know you've moved or deleted the music. It will still show the names of the songs in iTunes but if you try to play the songs it will ask you to locate the music.
Since I only use iTunes to listen to music, and have the iPad/iPhone/Apple TV devices to consider, I don't feel a need to use one of the 3rd party programs I mentioned earlier. YMMV