Crew Swap?!
After the universe was saved, Kirk and Sulu had an emotional goodbye via the view screen. If you pay attention to the background, nearly all the important crew members who were originally aboard the Enterprise are now aboard the Excelsior!!
Don't believe me? Watch that scene again. You'll see the older blonde woman and the guy with the blueish skin aboard the Excelsior.
It makes no sense. Was there a crew member swap between the two ships?