The crown and hands are the parts that suffer most from wear and corrosion. These watches are 70 years old and at some point of time they may had to get service that involved replacement of the crown. Remember that these watches were worn by divers in WW2, so they were used quite extensively.
IMO both crowns are 'correct', which means they are both Rolex, perhaps the bigger onion type was the one originally delivered with the watch.
Cheers and best from the holyland,