After I waked up this morning, I was looking at DCA-SFO-PVG-LAX-EWR-DCA itinerary for $600 leaving tomorrow. But I was astonished that I was able to book IAD-PVG/HGH-HKG-GUM-Canada city itinerary for travel tomorrow. The latter was more than $200 cheaper with slightly longer travel time and mileage. I was more astonished that United asked for volunteer for the first segment when I checked in. I guess that the cheapest booking code (G) was open long enough to let me book this itinerary.
Keep checking and be ready to travel the next day!