They don't know. Nobody does until the bill is processed. There are a thousand factors that might affect your coverage. This is the nightmare I'm living through right now. Even if you have the code and doctor and patient the help desk at the insurance company can't say for sure if they will cover it or not. That comes down to the discretion of the claims adjuster. You won't know if something is going to cost $100 or $10,000 until after it is done.