Regarding bodily injury vehicle insurance (not collision), and in the case where a household member, John Smith, whose car insurance agency, for various reasons, marks another household member, Jane Doe as "deferred" (IE not covered) on John Smith's vehicle policy, and Jane Doe uses the vehicle anyway (with permission of John Smith), would Jane Doe's own bodily injury policy (different agency/vehicle) still cover Jane Doe while in a car that is insured by John Smith's agency?
For some reference, I've read in many places that bodily injury coverage still generally follows the operator/borrower of a vehicle, but usually as secondary coverage. However, I have an insurance agency telling my household members that another household operator (that has their own policy on another vehicle) cannot operate the vehicle AT ALL if they are marked as a "D - Deferred Driver" (one of 4 possible household member types), even though ironically neither policy has collision.
This may be specific to Massachusetts, USA, as they require you to list household members, but I have a feeling it would apply in most places in the USA as well. I'm assuming this would be similar if someone borrowed a car in New Hampshire, where carrying insurance isn't a requirement, and the owner may not have insurance, but the borrower may for a different vehicle.