This is about the second edition of a book, i.e. an updated version, not a sequel or a second volume.
There is no particular reason to refer to the first edition now, since the second edition is the same book. The second edition brought the book (originally published in 1991) up to date for 1996, and it is in a sense still current now, because the language hasn't changed since then. The update added the SML Basis library which was just being standardised, plus better coverage of modules.
