Ah, I gotcha; I haven't looked at those settings in quite a while, since I haven't needed to alter them. Indeed, I used the default, ID3v2.3 UTF-16, because there are some foreign characters we use, mostly accented vowels. I don't know if v2.4 is supposed to be any better, and was thinking about using it, but when edited in iTunes, the tags became v2.3, so I stuck with that.
But yeah, you pointing out the non-standard extended tags that were in these files will lead to a lot more cleanup, so you've given me a lot of peace of mind thanks to that eagle eye. I want these files to be as close to perfect as I can get 'em.
EDIT: EVERY miscellaneous non-standard tag has been removed.