Backwards compatibility is kind of a pain. You have to make sure that every dumb bit of bad code you made before can be migrated to the next, slightly-better-but-still-bad code. But it's a necessary evil for gamedev, unless you want people complaining that they lose their save every update. I know not a whole lot of people play my game Isotopeia, but I have a decent chunk of lines dedicated to just making sure old saves work. Eventually I gave up with the oldest versions (which utilized a terribly inefficient function named countOf) and just decided to auto-reset the save if it's that old and attempting to be migrated to new versions. It's not like anyone played back then either way.