Parts in POIs - Not Showing; Not Resetting?

[Deverezieaux]

It is sounding like the only way to give Parts a chance to appear is to use RWG.

I think this is a question only someone at TFP will be able to answer. I think @zztong is spot on, that the probability is rolled when RWG is run, and then the parts become "static" to the world like the POIs they are in. This may be totally incorrect, but as prefabbers we have limited visibility into how certain things function.