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As you likely know, Adobe is continually updating Photoshop CC. But unlike in the old days, they're no longer assigning new names to the program each time the make updates. (In the past, it was easy to distinguish each new version of the program because it was named Photoshop CS4 or CS5 or CS6, for example.) For the foreseeable future, Photoshop will be called "Photoshop CC," but the program will be evolving even though its name won't change.
You can see Adobe's list of all the recent Photoshop changes here:
The book you own covered all the features that were introduced when Photoshop CC was first released in June 2013. As you can see from that list of updates, Adobe has since made various changes to the program. The new edition of the book covers all the changes through June 2014.
Bottom line, the book you have should still be quite useful. However, it doesn't cover any of the changes that Adobe has made to Photoshop CC since the book was published last year.
I hope that clarifies things for you.
Associate Editor, Missing Manuals