Again: how would you tell the difference? Say the process could have happened the night before, and the person who was supposed to do it decided to do it or not

Again: how would you tell the difference? Say the process could have happened the night before, and the person who was supposed to do it decided to do it or not on a coin toss. There is no way for the person who wakes up to know whether or not the process happened. That means that one time out of two the person would be "you" in your sense, whatever that means, and yet could not even tell for sure. You're talking about something you can't tell whether it is the case or not. It's an illusion. A copy is not just a copy. It's as good as it gets.