I think they calculate percentile based on the examinees of the same test. The October is a difficult test and even if your raw score is low, your scale score and percentile might still be high, cause you will be compared with people taking the same test. My raw score is only 56, but my scale score is 880. For the GR0568, raw of 56 is only 840. So if you retake the test and feel you do better, this does not necessarily mean you will get a higher scale score since other people might also do well as well.