As usual, you're correct, W. There are in fact a couple different variations of the Nautilus Jumbo rep in existence. One version of this rep has screws holding the bracelet to the case instead of pins (it should be pins), incorrect case details/shapes, bracelet details, etc.
The MBK with the slim profile lugs is the one to own (in my opinion).
Unfortunately my PP knowledge is limited; I am familiar with the Nautilus, and to some extent the Aquanaut family, and a few others, but don't know squat about the numerous other models they offer (like the Calatrava with numerous variations and models available).
I wouldn't mind having one of those nice 18k solid cased Calatrava reps, however...