How do the 1969 and 1979 books by Hopcroft & Ullman compare? Was the 1969 book an earlier version of the 1979 book?
1969: Formal Languages and their Relation to Automata
1979: Introduction to Automata Theory, Languages, and Computation (IATLC)
The 1979 book cites the 1969 book but does not describe how these two books generally relate. Looking at the Table of Contents, both books have 14 chapters and seem to cover roughly the same topics.
As a related topic: According to others (see the answer and following comments) and Hendrik Jan, the 1979 book is better than the 2001 (IATLC 2nd ed.) and 2006 (IATLC 3rd ed.) books; the 2nd edition "is geared toward second- and third-year students" instead of "fourth-year students and beginning graduate students" and "removed all the good parts", such as "the Myhill-Nerode theorem and several proofs".
