I thought the laws regarding the use of refrigerants were federal EPA laws and thus would be the same across the USA.
Federal EPA laws are minimum. There's nothing that says the states can't add on additional restrictions. California is known for it's tougher air pollution laws. Even cars have different emission requirements in that state than others.
I would agree, look for leaks and proper system operation before cracking the system to just add more. Washington state requires complete freon removal and leak check prior to recharge. more expensive that way, but keeps the freon out of the atmosphere and you shouldn't have to keep refilling it.