The Rotax engines don't have any changes that can't be ID'ed from the actual engine. (the year becomes irrelevant) So, the "Yellow" 587 are all the same... the "White" 587's are the same, the 657, the 657x, the 717, and so on.
So... if you need a gasket kit... just get the one for the engine you have.
Other manufactures change an engine during production years (Kawi 440 had a break in 79, and Yamaha had a 701 break in the late 90's) but SeaDoo was nice enough to just change the engine.
I guess I should add, that there can be RV and carb differnces... but the core engine stayed the same.