Best Practice - Multi-scene light/GI baking?

Hi folks

I've been reading up on baking lightmaps/GI for multiple scenes, and it seems the solution is to load all scenes that might coexist, and bake them as one (so that light influence can be detected between scenes).

In my situation, I have a scene for each section of a building, which is closed off by player-openable doors. So what would be the best practice here? If I bake with the doors in their default state (closed) then there would be no difference in baking all at once or a scene at a time (right?), as the light won't cross between scene to scene due to the door. On the other hand, if I bake with the doors open then I would get light spill on the GI even when the doors are closed?

My second sub-question, is that if it makes no visual difference, can I still bake scenes individually to cut down on baking time? If I have 10 scenes, baking 1 for changes in that one scene will complete must faster than baking the other 9 for no reason. It takes a while and unless I'm missing something, can't be done distributed over a network of machines?

My last related question - if I bake everything together, then bake 1 scene on it's own with its own lightingData.asset - what would take priority? Would the big-bake overrule, or would the individual scene bake take priority for that scene?

Any help or sage advice much appreciated!

Cheers

J