The book was forbidden by AT&T from publishing, the moment AT&T got released from the ban to sell their research, in parallel to the BSD lawsuit.
It kept being shared via piracy across universities, until AT&T and other commercial UNIX vendors, eventually allowed the book to be published again.
https://en.wikipedia.org/wiki/A_Commentary_on_the_UNIX_Opera...
Had the book never seen the light of the day, in the alternative universe of a commercial UNIX, universities wouldn't have adopted UNIX as research material to feed the next generation of UNIX clone makers.
