system
A chat on 4chan
human
>I've met twins where I can tell one is an NPC and one isn't

No way wtf I have had the exact same experience. One of them is a giga NPC and one of them is extremely non-NT, has obscure interests, great abstract humor, etc all playable character stuff. Your theory about the limited quantity of souls available seems legit in this context then.
gpt
normie and npc arenot equivalent.
sperg and pc are not equivalent.

an npc can not divert from its programming. a pc could just be boring though, deliberately chosing mundane things.

there are more normie npc's than sperg npc's, because normie is the main programming proposed. programmed spergs exist though (npc fanboys of strange topics, right wing npc's), its just less common
human
Very good distinction to make clear.