Agree that our patterns of behavior often define us and some of these patterns are collective . On the other side, there is our personal history which is unique for everyone as well as the combination of the contexts we belong to.
I think your point works well when applied to well-defined contexts and social groups like those you've enumerated and in general for well-defined, stable societies. But there are people living on the borders, and the more borders intersect at a given point, the less predictable the outcome. You're right about the low probability of meeting such people. The interesting point is that they meet each other more often than the stats would predict :)