Sql to reconcile Receivable Invoices' balances with their applied receipts

So, I have constructed a sql query to look at Receivables balances using ra_customer_trx_all and ar_payment_schedules_all.

I have another query which I tried to summarise and compare, to reconcile the unpaid element of the balances. So taking sum of receipts from the original invoice value and hoping to get the same figure as ar_payment_schedules_all for the outstanding amount. This query uses; - AR_CASH_RECEIPTS_ALL

This works in the majority of cases, but in some there are differences.

Is there another table that would give me 'other adjustments' or similar to the outstanding balances figures which would allow me to wholly reconcile the figure in ar_payment_schedules_all?