Why do all the Nick's rats look the same?

[A-train]

I think I must be going crazy or something, but they all seem to be the exact same! D: Is there a reason for that? Also, they don't show up in the archive. Is there a reason for that, too?

[Coalchaser]

Nick has not added the adult stage(s) yet so they are only temporarily in that stage. There are a few Nick rats that are PPS, however, so not all of them are the same.