If you zoom in too much, it becomes hard to make an unambiguous break because the code pased from hand to hand so much with overlapping groups of people...
And that's the real issue with any of these. At one point does one stop and another start. The people were pretty free and we all moved around. I do tend to think of FreeBSD and NetBSD and the follow on too much of CSRG and frankly, while they are different, they were more similar than different (FreeBSD focused on x86 originally and NetBSD was a little less polished in those days but worked on more HW).
At some point, you are picking nits and it really becomes more opinion/what you value than anything else.
I also think some of BSD (people & IP) leached into Research and vice versa.