The curves are set for whatever test that is being held that month. Collegeboard reviews the questions on that test and sets the curve accordingly. It would be ridiculous if the curves were arbitrarily determined. I'm sure there are more than a few people on this site who have familiarized themselves with the SAT well enough to know which exams are considered hard and which are easy. Having done multiple practice exams, I can honestly say the October math portion was ridiculously easy and I highly doubt they will curve it generously.</p>
<p>I recommend reading the link tokenadult provided if you are interested in seeing how College Board handles score equating. They don't curve according to how a group of students did on an individual test date.</p>