GP 2010 Historical Aged Trial Balance report = debits + invoices , less credits and payments?

So Im building a query that looks at data in GP to reconcile invoices with outstanding balances.  Disregarding invoices for a moment and starting with just the AR tables (RM10301, RM20101, RM30101 ) , the total on the Aging report (doing just a summary) is not even close.  What is the aging report doing other than the following:
( Debits + Invoices ) – (Credits + Payments)