I checked the backup drive, and I find the same errors. Those files have the same tags. I run a backup every night, and the routine prunes the versions regularly. The pre-tag versions are long gone.
Yes, these files are typically downloaded via BitTorrent (live ROIO's). I have considered the files were not completely downloaded or were corrupt in the source, but I am not sure how to determine. The original DL source is no longer available to download. The BT client confirmed the download when I first pulled it, for what that's worth.
I should mention that I tend to do a lot of tagging, and I wonder if I am causing some trouble using non-standard fields or perhaps too many fields. It sounds like FLAC files don't like ID3 fields being added. Whether or not I can fix existing corrupted files, I would love to know that my tagging practices conform to some sort of best practice.