Quote Originally Posted by XanBcoo
I'm pretty sure that if the Kurosaki family was one of the 4 families, people would have made a bigger deal about Ichigo Kurosaki running around Soul Society causing so much trouble. I don't really recall anyone saying anything to the effect of "Ah, he's a member of that family" either.

It is a possibility that Isshin changed his name, though. After the Kuchiki, the Kukkaku, and the Shihouin, there's still one noble family left to be revealed. Makes you wonder.
Maybe when isshin got married he took his wife's surname, and so ichigo as well