I think I understand, and I apologize.
If I understand the question correctly, it is about the extent to which coverage exists in regular insurance policies--home owners, commercial buildings, and so on. Virtually every single insurance policy has a nuclear exclusion. This allows insurance companies to dedicate their available capacity for nuclear liability to the operator's policy through NIAC. That way they're aware of what the exposure is right up front and it will not be claimed for under residential policies and commercial policies and so on. The available capacity is channeled to the operator.