It used to be the case that, with the exception of E deck cabins, if you pre-registered at anytime you would almost certainly get the 35% discount. However, it would seem that (because of the volume of pre-registrations now happening) if you make a late pre-registration, you can find that the discount for a number of cabin grades will have dropped by the time your turn comes around. This is when it can pay to check the cost of a higher grade cabin as eg a cabin on deck C may be less than one on deck D because of the different discounts available at that moment in time.