I don't know specifics about the USA, but certainly in the UK, private healthcare insurance works like most other forms of insurance, i.e. Pre-existing conditio

I don't know specifics about the USA, but certainly in the UK, private healthcare insurance works like most other forms of insurance, i.e. Pre-existing conditions or other relevant information is either not covered or must be declared and will be used to adjust premiums. No car breakdown insurance lets you take out a policy to cover the vehicle after it has already broken down...