I'm curious about this line of thinking. Do you think your specific consciousness was being held in reserve somewhere, and it would have been placed into a mortal body regardless of when you were due to come into being? Plus if your grandfather had stayed in Cuba, who's to say your parents would have still met, started a relationship, and conceived a child?
The way I see it, I only exist because of the exact series of events leading up to that one moment where I was conceived. I exist because of a combination of a specific sperm and a specific egg. All sorts of factors contributed to all of us getting extremely lucky, even up to the final hours, minutes, and seconds before fertilization. We won, and we denied a countless number of other potential minds the privilege of existence.
There's no way to prove it of course, but I feel like a different sperm being responsible for fertilization would have meant I would have never existed at all. My parents would have had a different child with a different consciousness. Even if a specific consciousness is tied to the egg itself, that gives a window based on the menstrual cycle.