User blog comment:Argorrath/Treyarch releases a BO2 teaser video called "Origins" for DLC 4/@comment-9261790-20130811170927/@comment-3463306-20130811171258

So the Zombies came in Der Riese? Nacht Der Untoten begs to differ. Dempsey also mentions knowing Richtofen before Shi No Numa, but not remembering, implying their memories were wiped.