Happened to me too, I was out shopping and I met Derwin and Frita and I FREAKED because I had two free spots I was keeping for my dreamies... turns out they can still randomly show up until they've left more than 16 villagers ago
Yep, I currently have over 10 villagers wandering around my main street. Some of them I enjoy seeing again. Others...I LET YOU MOVE FOR A REASON PIETRO! XD
My first town has only had 3 move outs. The villagers don't show up on main street. You have to have 3 or 4 movers before they start showing up. When people would talk about moved villagers on main street, I didn't quite understand what they meant. Then I got a second game and went through a bunch of villagers. Theres a ton of them walking around my main stree.