That depends on whether you have found a village or zombie villager to cure though. I've also somewhat iffy on breeding cells. For some weird reason or another they will escape structures or part of a machine without much explanation. Magicly finding there way out of sealed off rooms wandering about in the redstone. It does seem to be on vanilla's side. I found this happening often when I made an iron foundry where villagers important to the foundation of the workings would dissapear, despite being named/ encased in blocks to contain them. It's why I tend to stick to spawners for villagers. Any other mob like endermen or pigmen I feel work well. Squids and villagers are just the two mobs that seem wonky.A simple villager breeding station could be made. Have the baby villagers drop out of the range of the "village", which then pretty much unlocks the spawn limit on them. Might get stupidly laggy, but it'll work.