What are the design rules for using one safety valve and having another as a backup?

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After numerous safety inspections and project designs, many design firms now install one primary safety valve and one backup valve when designing such systems, along with auxiliary manual valves. However, there are differences in setting the operating pressure of these safety valves. For example, if the operating pressure is set at 0.5 MPa, both the A safety valve and the B safety valve are set to this value; yet the manual valves before and after the B safety valve are closed and sealed, so that it serves as a backup for the A safety valve； Another design concept is to set the A safety valve at 0.5 MPa, and the B safety valve at 0.6 MPa as well; the manual valves before and after the B safety valve are kept fully open. This is done so that, in the event the A safety valve activates and the pressure inside the device continues to rise, the B safety valve will then activate to protect the device. I think both of these concepts are valid, but I lean towards the first one. Which design concept do you think is more reasonable or more accurate?