I am still not getting this yichus thing.
If you are descended from Rav Yosef Karo, that is not a big deal. He lived in 1488 and presumably has hundreds of thousands of descendants.
Even if your famous ancestor is only 200 years ago, he still would have thousands of descendants, if not tens of thousands.
Really, for it to make you unique at all, it needs to be within the last hundred years or so.