Hmmm actually in this case I might recommend you go for the later book, especially if they cover new features in addition to the basics (I haven't looked at the InDesign CIBs in a long time). There are a number of new things since 2015/2017, including column rules, paragraph shading and rules, Import PDF comments, Adjust Layout, Endnotes, the Properties panel, and more. To see all the new features added in each of those versions, check out James Wamser's PDF available online as a Publish Online document:
https://indd.adobe.com/view/0fe50e63-71b1-4db5-91c1-c8f6c4738df2
Or, if you're just trying to remember how to get text and images on the page, how to use masters, styles, and other basics, then the 2017 edition should be okay. The major difference in interface would be the Essentials workspace that you're used to is now called Essentials Classic. The old "Essentials" workspace now looks really different because it uses the new Properties panel instead of the Control bar. The other big interface change that comes to mind is the new in-app font selector, which you'll see pop open when you choose a typeface from any of the panels.
If you can watch my New Features vids for InDesign CC 2018, 2019, and 2020 on Lynda.com/LinkedIn Learning -- just the videos that deal with the interface and features you're interested in -- that should be be a big help too. If you're not already a member you can get a free 30 day trial here (moderators feel free to delete, you can PM me here for the link): http://bit.ly/linkedinlearning_AnneMarieConcepcion
I have not seen the 2020 CIB for InDesign so I'm not sure if they cover all the new features.
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