The answer needs to come from your state DMV. Originally when the motor passed final inspection it was assigned a serial number. At the time the car was assembled this number was stamped into the top of the left frame rail at a location just behind the cowl where it was not visible without lifting the body. The number from the engine was used to identify the car. When the engine was changed the owner was supposed to notify DMV of the new serial number. Some rebuilders simply stamped the old number into the new engine. To tighten things up most DMV's began assigning their own number which was on a plate they attached to the door jam. In California at least 40 years ago if your engine number matched the paperwork they would just add an identification plate without a lot of questions. If it didn't match they would ask you to unbolt the body and lift it to see the number under the body. The actual term VIN originated in the fifties when the automakers/government got together and established a formal numbering system to be used throughout the industry.
That plate is an after market plate that now has the "vin".
