I am not sure about there being enough bolt above the plate...I am sure that there is a whole lot of hole for the bolt. The hole is permitted to be 1/16" larger than the bolt.Maybe the bolt doesn't project far enough above the plate for the threads to catch once a washer is installed?
The picture has a TPR-valve one would find on a water heater, not a conventional pressure reducing valve. It even has the BTU limits on it.P2903.3.1 Maximum pressure.
The static water pressure shall be not greater than 80 psi (551 kPa). Where the main pressure exceeds 80 psi (551 kPa), an approved pressure-reducing valve conforming to ASSE 1003 or CSA B356 shall be installed on the domestic water branch main or riser at the connection to the water service pipe.
We have some areas in the city that the operating pressure is 90 to 95 PSI