They may not, but there's so little original UNIX code in *BSD these days that it does not matter, in fact that's one of the main reasons they won the lawsuit in the first place.
I just opened my Red Book and reread «Short history of UNIX».
Berkley University bought license for AT&T UNIX[1] in 1977. They started to develop their own software for UNIX and distribute it, so this variant of UNIX is called BSD. Then they decide to remove and rewrite original AT&T code, due to license and associated costs, and released 4.3BSD[2], which then used by BSD flavors.
So BSD is UNIX, but it contains no AT&T code today.
Yes, my point is that since *BSD does not contain the original UNIX code anymore, it is no more UNIX than Linux is, since it was basically rewritten from scratch.
I understands your point but it's wrong because UNIX is system, not a single component. UNIX was generic name until it trademarked. See books, see complete code: http://minnie.tuhs.org/cgi-bin/utree.pl . As you can see, BSD UNIX still contains lot of code from BSD UNIX.
