United.com offers TIMATIC access.
https://www.united.com/web/en-US/app...aspx?i=TIMATIC
After entry of US to Japan via China, the following appears:
China - Transit Visa
Visa required.
Transiting without a visa is possible for:
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Nationals of USA holding confirmed onward air, cruise or train tickets to a third country, arriving and departing from any one of the following locations: Hangzhou (HGH), Nanjing Lukou (NKG), Shanghai Hongqiao (SHA) or Shanghai Pudong (PVG) for a maximum of 144 hours, starting from 00:01 on the day following the day of entry.
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