So, let’s clarify.
There are an infinite number of parallel worlds that we slip back and forth between. Obviously, since there are an infinite number, there are a (near)infinite number that are nearly identical to what we could call our base universe.
Sometimes the differences are almost imperceptible - your keys are on the table, but the fob is upside down in the one, right side up in another. No one even notices those changes.
In some the changes are more obvious - you keys are now in the foyer rather than the table. You “know” those are wrong, but you can’t prove them.
Then there are the Mandela-level changes. A significant chunk of the population sees the change in (nearly?) the same way. Berenstain/stein bears. Everyone remembers the *same *alternate ending to Big. Everyone remembers Shazzam.
But, we must ask, what about the really big (no pun intended) changes? There must be universes that start to differ in large ways. Maybe the manner in which we slip between universes only allows switching between universes with .99999999% correlation. Maybe we can’t end up in a universe where Hitler died as a child, where the dinosaurs never died off, where Schwarzenegger became President of the USA.
But how often do we switch? Minute by minute? Daily? Weekly? Eventually someone should cycle to the ends of the bell curve. You might not notice it on any given switch, but eventually .9999999% correlation over a number of universe switches means first you have Big, then you have Mandela, then you have Hillary as President. And then you have a universe where YOU weren’t the same.
And what happens if two of you end up in the same universe at the same time?
Maybe that explains mysterious disappearances like Judge Crater. He jumped to a universe, but no version of him came into ours as a balance.
And an indicator of a switch isn’t just clocks losing seconds. I think that flicker of motion in the corner of your eye - that’s a person that was in the universe you came from, but not in the one you moved into. Watch out for them!