Drakador_Chaos It's just random stuff, like file renames I forgot to add to the upgrader, strange logic that it doesn't know how to upgrade, and uncommon special-case situations. Also, sometimes when it has to generate a lot of code (like upgrading the operational logic or crew priorities), the result may work fine but not be ideal or the prettiest way to structure that code, so you may feel compelled to go in and clean up after it.