The beauty of the license exams is that they are not trying to trick you with material you've never seen before. In fact, they go out of their way to publicize the questions for you ahead of time.
You can actually see all of the exam bank questions at the ARRL website. As of the time of this post, ARRL provides the following schedule for when the exam questions will change:
TECHNICIAN Class (Element 2) Pool is effective July 1, 2018 and is
valid until June 30, 2022.
CURRENT GENERAL Class (Element 3) Pool is ONLY valid until June 30,
NEW GENERAL Class (Element 3) Pool will be effective July 1, 2019 and
will be valid until June 30, 2023.
EXTRA Class (Element 4) Pool is effective July 1, 2016 and is valid
until June 30, 2020.
The Technician pool was revised in 2018. The General pool is scheduled
for a revision in 2019. The Extra pool is scheduled for a revision in
2020. No question pools will be updated or released in 2021. The question pools review is part of a regular process. Each question
pool is reviewed and updated on a four year rotation.
That's not to say paper books are worthless, they are actually very good instructional manuals for principles that don't really change. I have a paper copy of the study guide for all three classes that I refer to frequently. Just pay attention to that exam bank schedule when you're studying for the license exam to make sure you have the current list. No point in handicapping yourself with things you've never seen before!
When I was studying for the exams, I personally used an app called Ham Test Prep. (I am not affiliated with the product in any way). It was a good way to get a bit of studying done while I was traveling.