We delete each past version of the game when the new one is released. The after-story parts are meant to be a little something extra for players who download and play through every new update, and that's the only way to not miss out on them (though Youtube videos also exist, I suppose).
You're not missing anything by not reading through them though. They're not integral to the main story, they're just a way to reward truly dedicated readers with a smidge of irrelevant content. =V