It appears this just comes down to inadequate inter-departmental accounting, not necessarily a net loss of any total amount of money, much less $21 trillion. T

It appears this just comes down to inadequate inter-departmental accounting, not necessarily a net loss of any total amount of money, much less $21 trillion. The original source appears to be https://www.forbes.com/sites/kotlikoff/2017/12/08/has-our-government-spent-21-trillion-of-our-money-without-telling-us/ https://www.forbes.com/sites/kotlikoff/2017/12/08/has-our-go..., which explains the situation better. For example: The report indicates that for fiscal year 2015 the Army failed to provide adequate support for $6.5 trillion in journal voucher adjustments. According to the GAO's Comptroller General, "Journal vouchers are summary-level accounting adjustments made when balances between systems cannot be reconciled." In other words, far more money goes in and out of the Army, or between its various departments, than its total net cost to the government, as one might expect for any large bureaucracy.