To add on to that, if you play 10-12 NONVUL and 15-17 VUL, would that be legal? At any one time, you only have a range of 3 HCP, but there are a total of 6 point-count ranges you can open 1NT with, as well as a total of 8 point-count ranges between your lowest and highest openings (10, 11, 12, 13, 14, 15, 16, 17)