NPC village spawned with only a Weapon Smith and generic buildings. I added the workplace blocks for Farmer, Fisherman, Cartographer, Butcher, Leatherworker, Fletcher, and Tool Smith. I also built a wall around it. I have made ~10 trades with a them. Every time I come back to the village there are more and more Iron Golems. There are currently ~30 of them while I only have maybe 10 villagers. I have attached a screen shot that shows some of them. I have not done anything special to spawn them.