I don't understand talking about possibility when discussing the past. Probability reflects our uncertainty about what outcomes will happen. Uncertainty is a property of our understanding, not of macro reality. When looking backwards, we know what happened and what didn't, I happened (probability: 1) and those other worlds didn't (probability: 0). Saying "they could have happened" seems to me a sentence with no real meaning.
Even if you go with a many-worlds view, that only means that all things happened with a probability of 1.
Even if you go with a many-worlds view, that only means that all things happened with a probability of 1.