I have been doing a little research on time zones in China, and one of the few sources on the matter seems to contradict the tz database.  

While the database indicates there were multiple time zones until 1980, Guo Qingheng of the Chinese Academy of Science Time Service Center published an article in 2003 in which he states that primary documents indicate that "probably in order to comply with instructions from central broadcasters, after liberation [that is, after 1949] the broadcasters in each area very quickly changed their local times to Beijing Time, in order to express unanimity with the center."  And that "by the beginning of 1950, within a few months after establishing the country, the entire country except for Xinjiang and Tibet was all using the Beijing Time standard," with Tibet following in 1960 and Xinjiang by 1975 (Guo Qingsheng [郭庆生], "Beijing Time at the Beginning of the PRC [建国初期的北京时间]."  The Chinese Journal for the History of Science and Technology [中国科技史料]. Vol. 24, No. 1, (2003), p2.)

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