Oh jeez, this is hard to keep track off, i feel sorry for Dungeon. 
Edit: This can still be saved with some quick editing though. Perhaps we could say that a few zombies with the stage 2 had slipped past Nicholas as he's fending them off like a badass with nothing but a knife, and those few that did followed wright into said living room as you were getting shit for the barricades. Maybe? I mean that makes sense to me.