How to restore original official NPCs?

Hey, I hope you are all doing well

I was wondering, is there any way to restore original NPCs? I noticed that after some time of not playing within a certain world, some of the official NPCs/townies (for example Care Ren, Erwin Pries, Connie Fidential, etc...) are culled and replaced by other randomly generated sims... it's a small issue yeah but it bugs me cause I am a purist (lol) and I really like the designs (and punny names) of some of these official sims. 

Is there any way that I can restore them in game? I tried downloading them one by one from the gallery but that doesn't restore their respective NPC/townie roles in game.

Additional info : I have A LOT of active households, probably around 120ish played sims, and most of the playable sims from each pack still exist too. No mods.

thanks!