Other mistake: When the Janitor plays with Kelso 'double or nothing' for tossing the cotton ball a second time in the jar, Todd tells Kelso he now owes him $600, in the end it was $700. This isn't a 'double or nothing' amount of money the Janitor could generate. They started with $5, so the count would be 5 - 10 - 20 - 40 - 80 - 160 - 320 - 640 - 1280 and so on.
Other mistake: In the last shot of the final scene, when JD and Elliot start down the wheelchair ramp outside of the hospital, an "extra" woman walks right in front of them. She was nowhere to be found in front of JD and Elliot before they started walking - she simply appears in front of them and walks down to some paramedics holding a stretcher.