According to the 2014 statistical yearbook:
Explanatory Notes
8. Although Taoyuan County was elevated to the status of a city directly under the jurisdiction of Central Government on Dec. 25th 2014, according to DGBAS, the sorting principles of cities and counties of 2014 are still presented as former [in this publication].
In response, we have declared a new geo code under our "city" pattern for Taiwan (ITWN_^^^^). Use of the two geo codes will depend on the particulars of each dataset.
References