All the albums are missing Album Artist and the Artist tag is filled with other data. From my understanding of my collection it appears to be composer or other artist that have performed the same track.
Can this be coming from the YADB?
Not as far as I know. That should only happen if you select tracks and do "lookup from online database". Even then it pops up a box to confirm. I'm not sure what might have happened. *Maybe* your files have both ID3v1 and ID3v2 tags? I'm not sure which ones MC prefers if it sees both. Probably the ID3v2 tags, but I'm guessing again.
1. can you think of anything I could have done during the import process to cause these problems?
Nothing comes to mind. Everything I can think of, other than the ID3 thing above, would require action on your part; it wouldn't be automatic. But I might be missing something.
2. what would you suggest is the best way to recover my tags into the Library?
2.a delete the Library and start over?
2.b update Library from tags. Can it be done for the whole library at once?
Either way will work. Yes, you can highlight all files in the library and do update library from tags and it will work. It will take some time, as it has to re-read every file. But it shouldn't take any longer than a regular import would take.
A fresh import is appealing in this case though. Because it would be another try at doing it to see what happens, now that you are pretty sure that all of your tags are correct. If you have playlists set up, or other history in this library (ratings, play counts, and that kind of thing), you'll likely lose all of that when you do a re-import. You'll also lose any custom fields you might have set up, etc. But if you don't have much or any of that a re-import should be no problem at all. If you do a re-import, I'd clear the library first: File > Library > Clear Library . Then go back into auto import and set up your directories you want to import. It should then import everything rather quickly.
Brian.