You would think that July (maybe MAY---for people trying to stay in priority sequence) and august would have high curves just because people have more time to prepare, but over all i have heard that it all balances out, there are those who prepare more then others and so on. Whatever the reason is, friends of mine who took the paper pencil exam in april and august made the same scores; with their practice scores not increasing your theory would mean they would do worse in august. However, the only thing to fear with the cbt is a smaller testing groups then paper pencil and if you have taken statistics you know what that does. As sample size increases the mean of the sample test takers comes closer to the actual population mean.
JUST TAKE IT