I'm wondering what happens when, or if it's even possible if, a villager that moved from your town moves in from someone else's. If it's a different copy of the villager, are they allowed to move in? Is their history (their recognizing you, the letters they show, etc) combined with the one who moved out of your town? Or is it similar to visiting someone with the same villager as one currently living in your town, and they pass it off as deja vu? Or, can they not move in at all? Just curious.
You cannot have multiple copies of the same villager living in your town at once.
Also, different copies of the same villager will not share "memories". For example, if one villager moves away, and you get a different copy of the same villager later on, they will have no memory of you. On the other hand, if one of your villagers moves to a friend's town and later moves back, that villager will remember you.
You can not have more thanmone of the same animals in you town. You can have the same animals as someone you know.