"Inspectors are not required to perform disassembly of the vehicle to inspect the fuel evaporative system. Visual inspection of the fuel cap is considered part of the Fuel Cap Integrity Test detailed in Section 1.4.5, and therefore is not required on 1996 and newer model year vehicles."
Maybe somebody won an undercover case with a missing gas cap. Their argument would be that that popping open the gas door is disassembly.
only check gas cap seals on 95 and older. 96 and newer should (in theory anyways) should turn the check engine light on if the cap is missing or the seal is not a good one. i don;t check for gas caps on ois, ever. 95 and older yes, but never ois or 96-99 cars.