in the book it says both..... i have a german version and on page 220 it says: "the term we use for our overallearnings is mizuage (not to be mistaken for the mizuage ceremony). on the 7th of january the geiko with the highest mizuage of the previous year is officially valued in the nyokoba-school.in my first year i recieved the award."
she talks about the wareshinobu-to-ofuku mizuage (wich would be the mizuage ceremony) a little later
maybe its the same term for those two different things....
anyhow it would explain why arthur golden claimed that mineko iwasaki told him that she had the "highest mizuage"....and that he had it on tape
maybe she really said that, but he thought about the wrong "mizuage-meaning"