I was going through trying to clean up images tagged as both 1girl and 2girls, and somthing came up that I'm not sure about; which way do these cases go (IE, are they tagged as 1girl or 2girls)?
Two of the same person: IE post #1727482
Two different personas of the same person: IE post #1732407
Daimakura: IE post #1730609
Zoom layer: IE post #1729377
Faceless non-detailed background characters: IE post #1541794
I take it it's common sense that posts like post #1564031 are tagged one girl since it's more like a comic, and we're not tagging 2girls if the same girl appears multiple times in the same comic page in different panels. I do wonder about post #1697279 though; it's parent is marked 1girl, and rensouhou-chan is neither marked as a girl or boy itself, but what about a character like that being represented by a girl like in this case?
Either way, the 2girls wiki mentions dolls but none of these other cases, and dual_persona only mentions that solo shouldn't be used but doesn't mention multiple_girls/multiple_boys.