The NC pins (i.e. A1, A9, C4, C6, E2, E4, E6, F3, F4, G2, H1) are floating and not internally connected. Page 23 of the MAX77818 datasheet states, "N/C pins are left floating and can be connected at board-level if needed." The MAX77818EVSYS connects the A9 N.C. pin to BYP because you must go through the A9 bump to get to A8 bump on the top layer.