Here's something pretty cool that happened a while ago. Before The Last Stand update for Left 4 Dead 2 came out, one of the developers posted a Steam discussion for feedback. I suggested that they should add the armored box truck from Crash Course to the beginning of Death Toll, and JAiZ thought it was an interesting suggestion. Sure enough when the update came out, the truck appeared behind the downed trees in Death Toll! Of course, only after the update had launched, I heard a piece of dialogue I had never EVER heard before in The Sacrifice, claiming one of the survivors drove a truck into a lake or something. That obviously opens up a major plot hole. But then I remember that Left 4 Dead 2 has a lot of weird retcons in the Left 4 Dead campaigns such as objects missing or in different locations. L4D's consistency is kind of strange anyway, so it "kind of" works out in a weird way.