I have been going through the tags thoroughly, and noticed that the year tags seem to be unaltered (so far). I hadn't thought of looking at the modification dates as well; great idea!
Re: File names, I'm lucky in that regard. The files are named correctly and in the correct folder. The big issue there is the sheer volume of files. Although they're named correctly there isn't any real uniformity in the folder/file names. So even then, I'll have to go through each album individually.
The more I've dug into this, the uglier it's gotten. For example, I've found albums where the artist and album title are correct, but there could be as few as a single song with the wrong name. It seems so random. So essentially, I can't trust that ANY of the tags are correct, unless it's an album that I have the tracklist memorized. Although, now that you've suggested looking at the file modification dates, that could be a big help in that regard.
I do have pretty good backups, but those are all compressed files. I was hoping not to have to go that route, but it seems inevitable. So many passwords!
My plan at this point is to check those modification dates and seperate out the unmodified files. Then I'm going to use Picard to scan as much as possible. Then go to the compressed files. I'm still pretty bummed, considering how close I was to completion, but I'm no longer about to jump off a building.
I'll get there.
Thanks for your suggestions!