The "ahead of time" is probable. Knowing they would need to reroute passengers, they may have "zeroed out" the LAX ORD flight to accommodate the over flow. The extra inventory was not "public" knowledge, and would not have been known by the RCC (or by anyone else who wanted to book on that flight) to insure that they were used for the volunteers/reroutes and not taken by people who just wanted to change their flight.