That's a good question.

I stole some characters' clothes and they didn't respawn. But in other people's game, they did.

I stole Kells' hat in the previous playthrough and it respawned after few in-game days. But in my current playthrough, it doesn't.

All of them supposedly respawn, though, so far I know.

May I add a few more?

- Vault 81 suit (vault 81)

- Vault-tec guard armor (vault 81)

- Vault-tec lab coat (can be found worn by scientists around Vault 81. Not sure if this item can be found as loot)

- Diamond City guard armor set (around Diamond CIty)

Also check this out:

- DB Technical High School Varsity (DB Technical High School; appear as a loot, located on the top of a locker)

Yes, The Vault-Tech can spawn in normal chests/dressers loot. (as well as regular lab coats)

Side note: have found red/white letter jacket/jeans via Clothing Store, doubt it's the same as DB, prolly just missing the logo; similar to Atom Cats Jacket vs Leather Jacket.

euhhh....uniform / armor from the Covenant security?

Ah yes! These ones never seen outside the Human Error mission so far I know. I guess that's the only time you can grab one.

Do you mean the Red Varsity Jacket? With white arms and a letter on the chest? Yep, I got it from loots, but it's kinda rare.

They also can be stolen from John the Hairdresser in Diamond City. Someone else also wears this. He usually hangs around the Diamond City Inn.

EDIT: There's also a very rare outfit. It's called Red Checkered Shirt and Slack. Only got one in my previous playthrough by random loot. Now I don't have it anymore. Anyone have a tip, feel free to share around