From my understanding of the matter, if you withhold your scores on any MCAT say the April and then take the August and release your score for that exam, medical schools will see both exams. (It works the same way if you take the August exam, hold your scores and take the April exam.)
Be careful regarding withholding your scores. My friend took the April 2000 MCAT and withheld her scores. When she retook the exam and released her scores, both were released. However, with the AMCAS debacle this year, they claimed she never took the first exam. BTW, her first exam was a 27, her second one was a 24. Most of her schools only got the 24!