I have been an absolute idiot. In a frenzy of clearing out old documents, I deleted some Excel files which I wasn't supposed to. Like even more of an idiot, I emptied the recycling bin. Further proof of my idiocy is proved by that folder not being in my backups.
EaseUS Date Recovery v6.1 managed to recover the files in question, but they open with strange symbols. I tried the 'Open and Repair' option in Excel 2010, but both 'Repair' and 'Extract Data' but on some files the preview still shows funny symbols and in others it says the file is corrupted and can't be repaired.