I'm primarily familiar with BJ8s, but I believe the number you've found on the shock tower is some kind of internal tracking number applied by Jensen Motors during manufacture of the chassis. This number is not, to my knowledge, relatable to any other number on the car, such a VIN or body number. The number on the BMIHT certificate is the body number, which should be stamped on a plain aluminum plate attached to the firewall.
If the number on the body plate does not match the number on the BMIHT certificate, then someone has attached a body plate from another car.