Long long ago, in the first such event, I believe one or two things (and only those one or two things) had a 50% discount (when they said the max was 40%)

I have since stopped bothering because dice event is like 70% discount on all the stuff you get (thou you can't control what you get except for the exchange, it does give a few mood scroll tool). But the point is, it is very possible that different items have different discount cap, and therefore it might NOT be true that everything can be 10-40%.