Airline staff with British passport holder go to Japan VIA Shanghai

Hi,

I am airline staff and go to Japan from London Via Shanghai and come back to London Via Hong Kong from Japan. I can use staff tickets between London->Shanghai and Hong Kong->London and these tickects are stand-by tickets not confirm tickets. I will buy confirm tickets between Shanghai->Japan and Japan->Hong Kong.

If I want to use 72 hour visa free transit in Shanghai on the way to Japan, does Shanghai immigration ask me to have confirm tickets between Hong Kong->London on the way back to London?

Please advise, thank you very much