Gallery Sims - what does and doesn’t persist

So I’m testing out what “aspects” of a sim remain on them when you save them to your library, for example all purchased and even hidden traits remain on a sim, as do visible skills and career level. However, relationship values always seem to reset to some baseline value. Does anyone that’s decompiled the python code have access to how the game chooses exactly what properties to keep and remove (career levels, traits, commodities, relationship tracks, relationship bits, etc.)?