I'm going to be fussy the other way around now, because I've played in an emptied town with just one household and no new Sims moved in anywhere. Yes, service Sims were generated, but no one moved into houses. Thus, as you can see, I have the opposite experience.
The handful of tray families don't matter, they always stay in the tray/bin.
Well. I'm sorry you have to deal with such an annoying aspect, LaPaige. I don't know that we can help. By the way, it looks like you have Supernatural installed with the sp options available. I forget which packs you have...
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On an unrelated note, I'm a sleep deprived zombie today. Sorry if I seem off or something. Top floor is out of order. Maybe I need to stick my head in a bucket of some caffeinated liquid and let it soak.