Well, here are some data points for anyone else... for me this is the first and last booking with Shenzhen Air. I simply dont have the time to deal with all the errors and issues, and having to call for everything that results in endless waiting on busy lines.

1. Even if you add all your details (Passpport No, Expiry dates, email, phone, etc) to you booking you still cannot service your booking unless you have a milage account

2. Even with the milage account it wont work, unless your passport is more than 6 months valid into the future from the flight date (no one tells you that, its not written anywhere)

3. all the emails and contact forms are uselss. The only way is calling (No is above)

4. If all the above is setup, you may still not be able to get what you need, as you either travel with a minor, are in transit, have previously have a seat reseveration (that needs be cancelled, but impossible)

5. checkin opens 6 hrs before departure, so you can try checking and get the paid for seats (but again, wont wokr if a minor is part of the pax)