Nice article
Really enjoyed reading this article.
I worked in USL (Unix Systems Labs) as a MTS (Member of the Technical Staff) during the 80's and into the early 90's and one small correction is that Research Unix was not a product of USL. Research UNIX was actually a product of "Department 452" within Bell Laboratories and although many of the innovations that were part of that distribution made their way into the USL product, they were distinct organizations.
I look back at my time there very fondly, working with some of the smartest and nicest people.