[EarthlingSil]

Originally Posted by kovidgoyal

calibre will never give you files with a jpeg extension when exporting. If you still have the original library folder you can simply zip it up and restore it, as described here: https://manual.calibre-ebook.com/faq...ter-to-another

Alas, I do not, as it's on my old PC that has already been wiped and taken apart.

I was afraid something that can't be fixed went wrong. I'll just have to slowly rebuild my library I guess.