1970 Dart "Hidden" VIN Where's it at??

I had a guy from the state of AZ MVD come out to do a VIN inspection on my car so I could complete the title work. He checked the fender tag, door tag and dash tag, but he said there was one more stamped number on the body of the car.

He was sure it would be on the firewall or the core support. While there were a few numbers on each, none were what he was looking for.

Does anyone know for sure where they would be??:dontknow: