Yes, they do update the PCAT from that time period between July and September. It won't be too much of a significant difference, but Dr. Collin's releases updates due to the addition of newer questions.
With that being said, take the exam when you feel most prepared for it. Don't rush into it because each attempt is pretty expensive in itself, and why would you want to pay for a bad score when you know that you could take the test at your full potential instead and be saving money in the long run.
Good luck.