Thank you to @kennyb6, you have succinctly pin-pointed the issue, and cleared up my problem.
This is actually an extension to the graph provided by @andre.abotnes, Push-room-name-to-Ceiling but I found it didn’t handle Compound ceilings, so I thank him for the earlier work, and hopefully this provides a more generic solution.
NAME_CEILING_FROM_ROOM_NUMBER.dyn (47.1 KB)
BASIC_CEILING.rvt (2.1 MB)
COMPOUND_CEILING.rvt (1.3 MB)