I don't think the space of parallel universes grows as quickly as the space of what could be possible in reality. Hence, not every version of reality is represented in a parallel universe. Like the incompleteness theorem in math, there are holes in what is possible.
I don't see how there could be enough room in space in for the many worlds interpretation of quantum mechanics so I don't think parallel universes are even plausible. Spacetime is already big enough, and it gets bigger when you introduce different kinds of multiverse, but 'parallel' universes to me seem both impossible and intractable, they end up being extraneous and solipsistic (though a great source of many sci-fi plots!)