For content review, as long as you cross-reference the LATEST AAMC MCAT guide, you may be fine with older versions of the books. You'll just need to omit certain subjects from the old books (such as solids in the physics book.) You'll be short on biochemistry material. We made a major change to the second organic chemistry book by incorporating a significant amount of biochemistry.
The big difference between the older books and the newer books is found in the passages, particularly in general chemistry, organic chemistry, and physics. The newest books (2016 or later) contain several new passages as well as many that were revamped to have more research theory and logic-driven questions. The amount of pure math questions was reduced. We also made a concerted effort to have more topic-mixing, where for instance, the gases section in general chemistry has passages on gas effusion as it applies to a lung system. There is a great deal of physiology, biochemistry, and molecular biology incorporated into the general chemistry, physics, and organic chemistry passages in the current books.
Overall, if you can afford to get the newer books (or at least some of them), you really should. To save money, you can look for them used. You can find them used for a good price if you are patient and check SDN classifieds on a daily basis. Typically, the market gets flooded right after scores are released and people know for sure they don't need to study again.
