I went through the exact same situation with my 20 year old music collection and MusicBrainz Picard and unfortunately this is just the state of music piracy even now as things are rarely tagged correctly or come from compilation albums, sample albums, or are just obscure and don’t have the proper tags available on the service. This is why I don’t mind paying for music streaming even though I selfhost most other media formats because you can put in days of work tagging songs and still have a jumbled mess at the end (Picard’s tagging template is also a huge PITA to use with some obscure legacy language).