I do think you raise a good question. This is not like a concert, musical, play or other venue, where tickets are bought in advance, so a know number of seats that are needed or used very specifically in most cases. Not taking into account any 'packages', on one cruise we never went to any of the shows, and on the next we went to 3. My buying a package for drinks, etc. would have no correlation as to whether I go to a show. So is there a time at which before the show, that the reserved seats/rows would be forfeited. That would seem to defeat the purpose of privilege of not having to show up so early for a preferred seat.