User blog comment:Damac1214/Thoughts on the Black Ops 2 Zombies series/@comment-9645468-20130707184403/@comment-3967954-20130708150338

Nah, I'm pretty sure they were expecting to do more zombies maps, but I don't think they predicted it would be as popular as it was.

Keep in mind that "Lullaby for a Deadman" was recorded before Nacht, and didn't see full usage until Verruckt. I think a second zombies map was probably always in the pipeline.