We cruised in Febuarary 2004. We enjoyed and and decided to cruise again - but not until 2006. The 2006 dates weren't opened yet, they booked us on a 2005 cruise and told us we could move our dates with our discount intact.
The price, of course, will change, but they will apply 10%.
BTW, it was 10% and a $200 stateroom credit for seven night cruises, but only a smaller stateroom credit for three or four night cruises - no discount - when we sailed.