Oh I think its the thing at the end that says "If this person was to sit the Mathematics HSC exam, they likely would have received a Band X in this subject".
I think it is that. I think because every MX2 student gets that at the bottom of their results table on the morning they come out online. Also, I remember after results my teacher said that despite everyone in our MX2 class got E3 (dat 89 killed me) he was proud because we all got a notional Band 6 (actually I remember my teacher saying national Band 6 not notional, but he had an accent so hard to tell).
As for the cut-off, no clue at all. Its the hardest thing to determine. However I do know that for a student who got 63 in MX2, it said that they likely would have gotten a Band 5 in 2U if they sat the 2U exam.
Disclaimer: Not sure if this is the right thing someone (Braintic, Drongoski, Carrotsticks, Trebla) tell me off or back me up here haha.