China 144 hr free Transit visa - Traveling to Shanghai next month

I am planning to take a trip to Shanghai next month (July), I Work for the airlines and fly standby. We are fly from the USA to PVG then for our return route - PVG-NRT-USA. My question is, if we are flying standby and are only assigned seats upon availability, What are the proper documents that I need to show upon arrival to show when we plan to leave Shanghai? we will only be there for 4 full days upon arrival July 1-5th. I can print the Seat request itinerary for our outbound flight from pvg-nrt. Will that still work for me to receive the 144 hr free transit visa