Ngaire would be the best person to answer this. I can tell you, however, the four ways we've gotten upgrades. One time, we paid for it on board. Another time a one category upgrade was part of a "special" for those who got canceled on Renaissance due to its bankruptcy. A third time, there had been some "blunders" on a previous Radisson cruise, and Radisson offered us a two category upgrade on our next cruise as a goodwill gesture. Finally, we booked a "category F guarantee" on the VTC (Voyager) and this was one of the rare times when the "guarantee" method of booking resulted in a massive upgrade to category C. This is the "upgrade I wish hadn't happened" I reported on above, and the unpopularity of this "shaking cabin" may have been part of the reason it was available as an upgrade to us.

Hope this helps,
Richard :) :) :)