That is one rabbit hole that is not always fun to jump down but is at least interesting. We often think we are all so unique and “original” when that is just not the case most of the time. This can often be seen when someone ask their personal assist from there phone or other services a question and it comes back with an answer that had been ask so many times a human was put in charge of creating something witty and cleaver as a reply.
Even what appear to be nonpatterns create patterns themselves by trying to avoid doing just that. I wish humans where far less mathematical then they already are. The Birthday problem in probability theory is quite interesting. It’s been something I’ve not had the time to properly understand for a while now due to many restraints in my own time. It is quite interesting really then when yes you do find more or less clones of yourself expect maybe you grew up in a different town, different country, had a different upbringing. That plays in some factor that make you different from another.
I’ve seen a couple of people who appear very similar to me. Two of them even had the same name and one of them even was very successful in the field I wanted to get into. Granted I have a very wide range of interests so that not really shocking.
DNA itself while we like to think it’s some complex highly variable thing. Once you start looking into it and realize just how constraint it has become over humans exists and just how much of it died off during the first few decades it is alarming. Even more so when they start connecting the dots and can relate large numbers of people together due to someone like Genghis Khan. It than is not that shocking someone we come into contact with has run into someone slimier as ourselves. Earth is after all a very small speck of dust!
Oh, I suppose my doppelgangers in looks and in personality are out there, I've just never met them. And the one or two times where I reminded a person of someone else, it was maybe in one mannerism, or because I liked to write. Well, that's a pretty broad stroke right there!
It's true though, as more and more people mix with others, there's bound to be less and less uniqueness just because at some point, you do manage to hit all of the different various combinations. There's an amazing amount of variations, however, and even though two people may look the same, doesn't mean they think or act the same, or want the same things.
If you go back far enough, you will find common ancestors for whole swaths of people. Especially if there were plagues or wars or famines or natural disasters. The strongest, and probably the luckiest, and along with the divinely preserved tend to survive. All kinds of things narrow down the field, as you said. The human version of natural selection.
Still, I don't think you can say any two human beings are exactly alike. They can be incredibly close, but there will always be something that distinguishes them.