Save files are in the User folder in the C: Drive. When some games develop further into the story, sometimes programmers has to change some codings and variables in the game. If your old saves doesn't have those newly introduced attributes, using old saves won't work or possibly will give you error in every step of the way.
If the game's new updates are based on the old attributes old saves work fine with the new update.
Nobody can say except the developers of the game if the old saves work or not. But the uploader always make a clear note about with the new updates, "with what versions of old saves are compatible". So sometimes in some games occasionally you have to play from the start. But if you have to, have a quick read of the new replies after the new updates. Some users share their save files in this thread and you can thank them and use those saves. Always check the dates of the replies before downloading them. Because old saves could give you errors.