By all means get the most up-to-date versions of the books. There was a big change in the passages and biology-related material in chemistry and physics in the latest books. If you are looking to save money, enough time has passed that you can find used 2016 books for about the same price as 2013 books. It's not worth trying to save a few bucks and use the less current books. The newest books emphasize more experimental logic questions and data analysis questions. And based on the score people have been getting using the newest books (both the ones posted here at SDN as well as the ones in our course), they are highly effective.