Call back would be using Uncle Frank as a password in M-Corp. Call back would mentioning the OM song in at least 2 episodes last series. If he was an occurring character he would have to be more then what he was. while what he was in that episode was more of a call back. they basically just did the same thing they did in white hole. Lister reluctant to activate him, kryten assuring him it will be ok, talkie being coy about not being toast obsessed before asking the very question, Lister naming bread products he doesn't want. Thats the issue about bringing things back after they have left an impression. they tend to feel like revisiting the greatest hits.