Speaking at an event today sponsored by Eurogamer, Valve's Chet Faliszek said the names for DLC packs found in the Left 4 Dead 2 demo were spaceholders only, put there as a test required by Microsoft.
According to audio of the event, Faliszek said:
If you're reading in the forums and you're reading about the "Miracle" DLC or whatever, that's test code. To get tested through Microsoft certification we had to do test scenarios with DLC. We haven't actually come out internally with what we're going to do yet.
The pick-apart of the Left 4 Dead 2 demo also revealed references to the original survivors. While Faliszek didn't mention that when he explained the DLC file names, earlier in the talk he did say "They're not dead, so we'll see what happens with that. They're not undead either."
Big thanks to Owen D-J, Stewart M and David S for the tip on this.
EG Expo 2009: Valve's Chet Faliszek [Eurogamer]