Would appreciate clarification on proper application of relief devices.

What I think I know is:
1. For application on ASME vessels, relief devices must be certified by National Board.
2. Relief devices are certified for either vapor or liquid service and are not dual service rated.
3. Manufacturers of vapor service relief valves advise to "connect to vapor space".
4. A vapor service rated relief valve may self destruct if subject to alternate vapor/liquid exposure.
5. If both liquid and vapor are in close proximity to the relief device (as on oil pots and thermosyphon tube-side applications) there is a high probability
the device will be called upon to handle two phase flow and violate all above intelligence.

What am I missing here??