The U.S. Navy aircraft carrier shown in the rescue effort at the end of the film is the U.S.S. Coral Sea (CV-43). The only other identifiable U.S. Navy ship noted is the heavy cruiser U.S.S. Helena (CA-75).
When Grover is floating around in the balloon harness towards the end of the film, when he nears a building with a brick facade, you can see a shadow of the rigging being used above the balloons on the brick wall.
Shirley Jones' hairstyles during and after Grover's escapade, goes from straight/flat, to flipped up, to very wavy, back to straight/flat. Hair color also seems to vary.
When "Uncle" Cy is shooting at the balloons, he gets down to one last big red balloon, with Key's head right behind it. In the next shot of Grover and Key, there are now three balloons, one big orange one and two smaller pink ones