I mean, there's plenty of articles about how provincial governments have been caught falsifying economic data.
But I also found this...
"However, the NBS is aware of the tendency for provincial officials to overstate GDP, and the bureau makes corrections for this behavior. In 1994, the country introduced census surveys to bypass lower-tier statistical departments and check the quality of the data collection. Four years later, the NBS took action against data falsification by issuing a reform that allowed for statistical breaks in provincial numbers to relieve past exaggeration. In 2015, the NBS reported national GDP of $10.4 trillion, which was about 7 percent less than the sum of the provincial numbers."
I think its a good thing China is cracking down on such data falsification.