Two thoughts ...
1.) Lion's was not a general book. It really was more of a kernel 'here-is-how-the-magic-happens.' It's still the best I know for that. BTW: it did not leak. It was purchasable from WE. But the cost was high and it was hard to get (you had a price you had a license and could not buy/order it at any book store - I don't think it had an ISBN or a library congress number originally).
I know a couple of the schools (like CMU) wanted to use it for the OS course, but there was some hang-up associated with it in the mid-70s, which I don't remember - we did have a couple of sections passed out for a few lecture. But because of how it was bound (and short), it was photocopied s others have pointed out.
I think Michigan managed to use the whole thing for their OS course, as I seem to remember that both Ted Kowalski and Bill Joy got copies there (although my memory is that they both had photocopies not the original Orange and Red bindings). Ted brought it to CMU, which is how I first saw it (and I think my original copy was a duplicate of his). And I remember seeing a photocopy in wnj's office at UCB. The first time I saw the official Red/Orange bound version was when I ordered it at Tektronix from WE a few years later, but I had to leave it there when I went back to grad school.
2.) The question asked about general 'Unix' text -- my favorite is still Rob and Brian's and I still recommend it (particularly to learn how to >>use<< UNIX/Linux today by doing the exercises), but it was not first. Steve's certainly was early and I thought it was a good explanation and until Rob and Brian became available was what I suggested when people asked. In fact, early Masscomp system's shipped Bourne's text, until Tim wrote the original 'UNIX In a Nutshell' that started his empire. That said, I do seem to remember there was another book around the same time (79-80 ish) that had a light blue cover that came from one 'PC-press' publishers. I wish I could remember the author and the name. I remember looking at a copy in Powell's in Portland when it came out and not being impressed.