I checked the Table of Contents for you of both books.
The main differences:

In lesson 5,
The topic about Content-Aware Move tool became Content-Aware Fill.

In lesson 6,
The Select Subject features has been added.

In lesson 10,
The Kyle brushes were added.

Overall, the Classroom in a Books often don't cover brand new features in depth, unless they're really very important and life-changing. So you can easily use the older editions for the basics, and learn all the details about the new stuff from the New Features webpage and related Help sections at Adobe website.

Enjoy !


Oorspronkelijk geplaatst op Quora: Am I missing much if I get the Adobe Photoshop CC Classroom In A Book 2017 Release as opposed to the the 2019 Release?"