How Many Little Things Could Be Different From Reality to Reality?

i recently had a dream within a dream. It was so minor, but it felt like i flickered into the reality in which i did get upgraded and for whatever reason, moved out of that reality. I don't know if you've ever had a dream of something, and when you're waking up from dream, you almost wish you had proof of it. And in that case, i quite literally had the proof on my phone. So, like, stupid, obviously, like an upgrade on a flight is different. But it makes you think t like, how many little things could be different from reality to reality?