As with all statistics, there are discrepancies that from time to time may obscure the meaning or validity of the particular estimate in question. For the vast majority of the time, any such uncertainties amount to very little. Overall, harmony among the major accounts reduces the signal noise from any one featuring a significant inconsistency.

There are, of course, various economic areas where estimates are going to be questionable no matter what. For example, though we have what are taken to be solid figures on both sides of the Pacific, there has been a very large disagreement as to how much trade the US and China actually undertake with each other. The Congressional Research Service in March 2016 claimed:

From the U.S. perspective, its bilateral trade deficit with China more than quadrupled in value over the last 14 years, from just over $83 billion in 2001 to over $367 billion in 2015. However, from the Chinese view, its bilateral trade surplus with the United States increased nine-fold, from about $28 billion in 2001 to more than $237 billion in 2015.

No satisfactory answer has yet been found for such an enormous difference, though there are several candidates proposed. The report submits “under-invoicing”, the twin of Hong Kong “over-invoicing” on China’s import side, as well as “mid-shipment transfers in ownership resulting in the new owner adding a markup in the price.” There are also value differences, particularly where goods are shipped through third or fourth party countries and principalities (such as Hong Kong), which also has the effect of obscuring, for both sides, the country of origin/destination.

There has also emerged something of a further discrepancy from within the Chinese statistics. The General Administration of Customs (GAC) tabulates the monthly trade estimates for China, those that you see described every month in the mainstream media reports. According to their latest press release for the month of March 2017, Chinese exports rose 16.4% year-over-year. Though there are calendar and price effects to consider in that amount, China’s other government agencies such as the National Bureau of Statistics and the Ministry of Commerce which supplies the NBS its numbers for trade have over the past few months had them come out differently.