The only stipulations I have for Sterling II is that the date is the 15th of the month or later, you're on Dallas' path in Story Mode (which you are), and you've seen Sterling I (which you said you have). It's a scene that triggers on the main planner page... uh, maybe more important custscenes are happening (I doubt it ...) or you're in a weird lull period such as its Christmas-New Years (it should still work though??). If you're on skip mode, maybe try turning that off? It's weird you can't trigger it.