<p>There will be, inevitably, words that you don’t know on the SAT. There’s no way of “knowing all the vocab”. Also, some of those questions don’t even really test vocabulary knowledge as much as they test reading comprehension (some). There are about 12 questions or so that deal with sentence completion (correct me if I’m wrong), and getting all 12 right does improve your score by a lot. So yeah, relatively, knowing SAT vocab should improve your score, but that’s just the same as “knowing” the reading comprehension section and “knowing” the SAT Math section.</p>