I suspect that there are certain objects in the game that do flag as custom content, possibly when using debug or hidden object cheats, but I don't know for sure.
The reason I believe this is because I once used a single mod to unlock the hidden CAS wardrobes, made some Sims, removed the mod, and one of my households flagged as having CC. No matter what I do I can't seem to get the flag off. I don't think this was intended so it's probably some kind of bug, but still frustrating, as it's a full household of 8 Sims and I don't know what item is causing it.
