I didn't know that about American cars. I guess your perspective on the matter biases you towards thinking that the Chassis number and engine number should be the same number, but since we are talking about Japanese cars.....
When applied to the S30 "matching number car means" (at least to me it does) that the VIN Tag (Tag as in a metal plaque attached to a vehicle that contains information about that vehicle, irrespective of size, in this case I was referring to the one in the engine bay, yes lets call it the Nissan Identification Plate, or Nissan Model Number Plate, or any other name to describe the alumin(i)um plaque/plate/tag affixed to the engine bay), has numbers that match the chassis number on the firewall, and the engine in the car. Since the S30 has different numbers for chassis and engine.
Damn, now you have me sounding like a lawyer.
US cars did get this engine bay tag right?
From an Aussie perspective: We had the factory fitted tag/plate/plaque in the engine bay, and thats all. No VIN tag numbers on the dashboard, and no plates/tags in the door jamb. Though we did get an extra compliance plate in the engine bay, as dictated by Aussie law. This allow had the VIN number on it.