Hmmm. After having declared above "Yokohama" so confidently, I am now looking around for actual cruise documentation that states it departs from Yokohama, and I'm coming up empty handed. Maybe it's an erroneous assumption/belief on my part! Will revert if I find anything one way or the other.
UDATE: Just looked at Cruise Mapper, and it looks like we are indeed out of Tokyo. Yokohama has two other big cruise ships in on the 28th, and QE is shown as sailing out of Tokyo. Oh well, will have to make Yokohama a day trip then to explore, as I was really looking forward to it.
Thanks so much for calling this into question - we would have looked kind of silly showing up at the Yokohama terminal for the wrong ship!