I must be special then, because I have cancelled cruises before - including with NCL - and have done so prior to final payment due date and had all of my money returned including the deposit.
You mentioned a couple losing their deposit with RCCL. Here is the U.S. RCCL Link
which shows that all monies are returned if a 7 day cruise is cancelled by the 70 day window, and 60 days for 3-4 day cruises. Are you in the UK? That could be the difference. Also, the agency you work for may have it's own rules where they keep the deposit for cancellations even though the cruise line refunded it.