The assessment is based on a high degree of consistency across multiple authoritative sources. The Shanghai Futures Exchange is the primary source for this data, and reputable secondary sources that aggregate this data, such as CEIC and Barchart, are highly likely to be accurate. Crucially, a highly authoritative source, Bloomberg, directly reports on the slump, stating inventories have hit the 'lowest level since 2015.' This claim is stronger than the one being assessed ('since 2016') but fully supports it; if inventories are at their lowest since 2015, they are necessarily at their lowest since 2016. Even the low-authority source corroborates the general trend of declining stockpiles. There is no conflicting evidence among the provided sources, leading to a high-confidence conclusion that the statement is true.