At some point in the DMV system, there can be two plates associated to one vehicle. Certain new owner transactions, lost and reissued plates or simple administrative issues.
Not a criminal hit or anything - Sometimes owners who have held on to the old plates for one reason or another have not made the change over to the new plate. The vin is the best way to obtain current vehicle and registered owner information.
Subplate comes up on a DMV return to law enforcement dispatcher or MDC indicating that DMV has issued new plates on a given vehicle. Could indicate the vehcile is stolen ( cold plated).
Not heard often is a cold plated vehicle, (just law enf. slang) where vehicle has been stolen, with plates from the stolen vehicle removed and replaced with plates taken off another car. This radio term may be used when a unit runs a plate for example on a Ford, but the DMV record comes back Honda. Next thing you will likely hear is suspect at gunpoint, or a felony stop.
In my 15 yrs at a major law enf dispatch center these were as often DMV errors as the real thing. DMV on occasion sends out the wrong plates to people. Once it's all Code 4, and a check is made by VIN# I often came across the plate on the vehicle was one digit off what was in the system ie: SAM123, instead of SAM124.
Pretty embarassing after grandma gets stopped at gunpoint.