The US treasury also has another 400 metric tonnes stored in the New York Federal Reserve banks vault.
The bank states on its website that depositors will receive back the same bars that the deposit as individual bullion are unique, but when Bundesbank withdrew 5 metric ton's in from the Reserve in 2013, the bars they received had been re-smelted.
This is because although the NY Federal Reserve offers free storage for bullion, but they are actually leasing out their customers bullion. Maybe something similar is happening at Fort Knox, I find it hard to believe that anyone with a brain would allow that amount of collateral to sit idle when it could be earning billions.