Almost every ship sails 'full' or close to it. When people talk about filling the ship, they are talking about selling it out at 'full' price. Unsold cabins are filled by discounting, some of which is not visible to all. TA's have clients who can sail at short notice at the right price and this fills unsold cabins.
An old rule of thumb is that 80% of cabins sold at regular prices meets the costs of the cruise, the other 20% can be filled below 'cost' as those passengers will drink, take excursions etc which provides the all important revenue.
I have been receiving emails from RC once or twice a week for months offering special deals - they are always for Quantam out of Brisbane, not for Ovation out of Sydney.