Just checked my spare luggage labels from last year, and they are printed on both sides of the label, one side shows the Cruise No. and Booking Ref, the other my Name and Cabin No. Please re-check yours, if these details are missing get in touch with your TA, or P&O if you booked direct to get this sorted.
When you arrive at the port, your cases are taken off you and transfered onto the ship and taken to your cabin. You will then go through to embarkation. We never got our cases until 8pm. This was because the ship is so big and has a vast amount of luggage to load onto the ship and transfer to your cabin. Your cabin number is on your luggage label, check both sides of you labels. Leave your labels on your cases for disembarkation, beause they're put on the dockside in groups by label color, making them easy to find.
Our cabin number was printed on the label, you need to contact P&O and write them on, clearly. We received our luggage within an hour of boarding.
If you suitcases are not easily identifiable (and how many of them are?) tie a brightly coloured ribon or tape to the handles, or buy bright luggage straps to make identification easier.