Most states and carriers do not allow duplicate coverage, however in some instances it may be allowed based on certain criteria. For instance, you as the child are a student away from home at school with the vehicle there are policies in some states that may be purchased to cover that risk with both you and your parents having policies on the vehicle.

Also if there is more than one owner to the vehicle there are carriers that will allow multiple policies as the co-owner may wish to be certain that there is coverage on the vehicle at all times since they can be held liable and in many states penalized with the primary driver if insurance does lapse.

The insurance policies involved with dual coverage would outline the terms of the policy and how claims would be made. The insurance companies of course should both be aware that additional coverage exists. In this case there may be several factors that determine what is or is not covered. I would suggest that the policies be reviewed and that you seek the advice of your insurance agent or of the insurance provider to make sure they understand there are 2 policies on the one vehicle and that they allow this. If they do then next find out how claims would be placed for each driver.

What Mercury may be telling your mom about her policy is that if you were in an accident since you are not listed on her policy she would not be able to place a claim through her coverages, instead it would need to go through your PGAC policy. Your mother would need to clarify with Mercury but it appears they would not cover you if you are the driver or household resident and not listed on the Mercury policy.

Since having duplicate coverage (two coverages for one car) is abnormal you and your mother will check with your insurers to make sure they both allow this and how claims would be processed when you or your mother are in an accident.