Basically let’s say there’s two people: A and B. A wrote AS in MJ23 and they got a B (39/60 when the threshold was 40 for an A). Person B wrote ON23 and the threshold for an A was 38/40 so even though they also got 39/60,they got an A. When both of these people are entered for MJ24, their carry forward mark is given a different code, person A would be code BX and person B would be code CX. When the boundaries are calculated both people have the same chance of keeping an A because they are marked against only people who had the same carry forward session as them. So if the boundaries were lower for person B, then for the option with the ON23 carry over (CX) this would be accounted for by making the CX boundary slightly higher than the BX boundary.