Books remained current for a longer time back then but it was already clear to me that they are not the way to go. Manpages were current. Experimenting is the way to learn stuff. Books as references have been basically dead since 1994 and the first websites with Javadocs IMHO.
The numerous similar books, now about Linux, that have been published in the first quarter of the 21st century indicates that your humble opinion is out of step with reality. (-:
I read Foxley's Unix for Superusers, the Unix Text Processing book, and a couple of other books.