In the first flashback, we see a meteor shower; since Shion was a contractor since he was born, this would mean that the false sky was already in place. To my knowledge, there are only two events that had a lot of contractors die (thus showing a lot of stars falling): One was Heaven's War, and the other is the events at the end of the first season.
When Shion's flashbacks occurred, was it during Heaven's War, or the end of the first season (which I like to refer to as Hell's War)?