For kindle, at least, authors can do an "optional" update or a "forced" update.

The forced one is pushed to every device automatically, and Amazon strongly warns against this when you attempt to do it, becaues it deletes all the readers' notes, comments, and bookmarks. It's basically suggested to only use it for book-breaking issues where the current version is essentially worthless.

The optional one adds a little update marker to the book in kindle (similar to a phone app) and lets the user grab it at their own leisure, or ignore it. It's highly unreliable, but is the best practice for any updates which aren't fixing a book-breaking issue.