China normally requires a visa. These are carefully checked including matching the passport photo to the visa applicant.
There is a special no-visa 72 hour transit arrangement for some cities including Beijing. This requires an onward ticket to even get onto a flight to the city. The visa / onward ticket status of both stolen passports will be known to MAS and will be very interesting whatever it turns out to be
China 72-Hour Visa-free Transit in Beijing, Shanghai, Guangzhou, Chengdu, Shenyang and Dalian