This is a common misconception.
Sold out categories can indeed be repriced. Royal does maintain a price for sold out categories in the event of cancellations.
Price drops can be category specific or across the board where they may see a sailing not selling and apply a flat rate % off of every category. This woukd be applied to sold out categories as well.
The best way to monitor this woukd bevto track a category similar to what you booked, fir example owners suite and crown loft suite. If you see a big price drop on a similar category it's worth a call.
I have had a price drop applied to a Royal suite and there is only one if those.