Managed to at least check that the booking exists--- in the airline Chinese website if I use my passport number and e ticket number it recognises the booking for seat selection purchase purposes on the Chinese version of the website. Unable to add my frequent flyer number etc, it's view only mode. Keying in the exact same info on the manage my booking section doesn't work (booking doesn't exist message), nor if you use the records search field (booking doesn't exist). Confusingly the English version flips the surname and first name fields Vs the Chinese version. Chinese version is Surname + first name whereas English version is Name + surname.

Shenzhen air and air china apparently do use the same contact centres overseas IE their London contact centre is for Air China as apparently they all belong to the parent Air China (air china still owns 51% of shenzhenair). But when the overseas offices are shut the phone redirects to Air China contact centre in China which refuses to assist with Shenzhen Air bookings but will give out the +86 local number for Shenzhen Air (need to use Skype to call).

The PNR doesn't work with check my trip nor any other non Chinese booking systems, they all say booking doesn't exist.