The void is where villagers who don't get adopted goes right? Once they go into your void, they are added in your pool of the 16 villager cycle, they might move in another town if you visit a town with 9 or less villagers without you knowing about it, so you can clear your void by visiting a town with 10 villagers, about the 16 villager cycle, all I understand is if you have a dreamie you want to get back, you will have about moved out 16 villagers (17 to be safe) once that is done the villager you want, will be erased from your void, and you can get the wanted villager back in your town.