I've read through some threads regarding this topic, and I'm now much more confused than before.
Before, I thought I understood: If you add a downtown, the second downtown will not add sims. I thought this meant that if you add a custom downtown that normally has some extra strays or npcs added, they simply would not be, and I could limit receiving duplicates in this way, by turning the second one "empty" through attachment order.

My initial intentions were to install a decorated Downtown instead of regular downtown. But since this decorated Downtown was almost empty, not empty, I thought I'd install a REALLY empty Downtown first, to avoid dupes. (Afterwords, I would add downtownies back through a subhood -- I wanted this method to have fixed face templates and restored character data to previously corrupt characters, rather than having an empty hood with few to no sims.)

But then,, I double checked to make sure.
And... I'm finding out that perhaps the creation of a second downtown doesn't suppress character generation? Does it actually kill sims rather than suppress generation?
Does an "inhabited" downtown that I read about before not refer to all the sims packaged in the downtown, but only to downtowns with packaged Playables, specifically?

What do I do? Are those extra simfiles inevitable, so I should simply download the Downtown I want without worrying about the clone population?
Or was the conflicting information I came across actually in the wrong, and my clever workaround could actually turn out well?

This is what I know about Downtowns, and sorry if this doesn't answer your question. I have three downtowns. They were all custom ones I built from scratch. I didn't add the pre-made Downtown, I didn't download any created ones to add either. I never had problems with dupe downtownies, killed of downtownies, etc and they seemed fine taking up apt residences in the different custom downtowns.

To clarify, I want to use a downtown someone else made, that has some strays, and a baby new year, and some other random npcs, attached, but I want to avoid having dupes of the pets, but especially of baby new year, since there's only reason to have one new year. I rather like the premades, see, and don't like seeing clones of them around,, because that cheapens them, I think. And I don't enjoy the sims I make myself, either, so I wouldn't want to have to makeover clones.

I'm not worried about the game creating new downtownies-- in my program files, I can replace the first downtown template with an empty one, or with a clean one, no issues.

What I'm concerned with is what is mentioned in this thread, https://modthesims.info/t/562049

reading this today, I'm comprehending better. I got confused by some of the discussion in the thread, but now I think I understand the conclusions better with fresh eyes, not getting tripped up by the arguments so much.
I'm going to assume my initial understanding was probably right, and not worry about it.

Thank you.

Update: Turns out, my caution was warranted.

DO NOT add a second downtown with npcs attached if you hate SimPE like me, because like Jawusa had said (I think), they become deleted rather than suppressed. I ran hoodchecker and found "has no character file", soooo... I'd better add that hood first, and tolerate the dupes. I don't like scrounging in simPE.

No biggie, I have the archived backup.

Updateupdate:
May have just been a bad hood. I tried adding it by itself, but it wouldn't copy the sims into the neighborhood properly, severing them even though it's the first downtown added. So I'll have to give up on it, sadly.