Does it matter? Even if it isn't the latest and greatest, it's still valuable for it's original reason: To teach you about the basics of constraint programming. And now it's valuable for a new reason: To teach you about the context and evolutionary path which led to modern constraint programing.

Often, the latest and greatest is defined in terms of incremental changes from the body of generally accepted knowledge. If you just read the most recent stuff, you'll probably lack the requisite knowledge to understand it. This is true up until the point that the new stuff becomes generally accepted and widely known. At that point, somebody writes it up nice, requiring minimal context, but by that time, it's no longer the latest and greatest!

Constraint programming was a big topic in the 90s. It has kind of tapered off as one since then. There are legitimate questions about whether it can scale or not to general purpose problems.