Itr is true, with separate files you can just open a later one. Either you have to save variables to say that you are supposed to open that one (except someone might be able to save that to) or you just have to not care, if they want to spoil it then they can feel free.
And yes, if you do use multiple files, you do have to change stuff in
every single file (if you want it changed in all of them)
See my post
here for my list of the pros and cons of various multiple level methods (although I didn't mention the problem above, about people just opening a later level.
An oversight.)