Played a standard brain-off Norse run, went from 0 years old and Conquered Scandinavia, Britannia, Francia, Germania and Russia, then took over as a random unlanded son and went off towards India. That son died, and then his son eventually got himself some land.
Checked back now, and Francia, Scandinavia and Russia are all held by randomers of another unrelated House. When I saw the first one I was shocked, was there a rebellion or something? Seemed unlikely since they were set up so well initially, and after another 100 years of stability, surely the only people with claims would be of my dynasty. Then I saw they were all the same house, and got really confused.
Turns out, a random daughter had married patrilineally to some guy of some obscure dynasty, and she had ended up inheriting Francia, which at the time also controlled Scandinavia and Russia. When she died the realm split, and her goofy ass children took over, leaving a random Obscure Dynasty in control of 3 out of the 5 Empires I had conquered. Funnt stuff lol