I agree. The thing is, with the chart provided, there doesn't appear to be any draw down of that inventory. Every year the apparent consumption is 7-10 million tons (or more) less than production+imports-exports.
Perhaps this is like the mysterous 2-3 million people who deplane in the US versus those who enplane to leave for overseas.
Every year for decades, 2-3 million more people have gotten off international flights than have departed on them.