Perhaps some others have had a different experience but the consular section of the Chinese embassy in the UK has never asked me to submit copies of my degree certificates or teaching qualifications to them in order to obtain a z-visa. They are primarily interested in the foreign experts certificate and letter of invitation. In order to acquire these documents from the Chinese authorities you may require a bachelors degree but they are not processed by the consular section of the Chinese embassy. Therefore I don't think you can count on the consular section as being a first hand source of information on this specific question. The decision to award the above mentioned documents is made at provincial level within mainland China and seems subject to change and interpretation without much warning or consistency.