The “sold out” category question with regard to bid upgrade programs is a source of confusion across all cruise lines that offer this opportunity.
It doesn’t necessarily have anything to do with current inventory, but more about possible cancellations later on down the road.
Example: We had a top level suite booked that we unfortunately had to cancel two days prior to sailing. Our cancellation then set into motion a host of upgrades from our high category on down the chain.
Someone in a lower category “won” our suite, then someone else won their now-vacated suite. So on and so forth it goes…
This is an excellent (and efficient) program for the cruise lines as they already have a host of bids for all different categories, along with your credit card number and authorization from you to charge.
So don’t get caught up when you see solicitations to bid for sold-out categories.