There are 3 types of creditor reconciliations:
Reconciliations for creditors on "pay-on-statement" terms
These are created using the creditor reconciliation activity. Invoice items which have been incrementally posted during the statement period must be manually checked against the items on the statement.
Implicit reconciliations for creditors on "pay-on-invoice" terms
These are posted automatically when clicking the 'Mark payable' button on a creditor journal. The reconciliation mirrors the invoice, and allows it to be paid immediately.
Reconciliations for purchase orders
These are created using the creditor reconciliation activity when a final invoice is received. The items that were recorded on the purchase order are checked against those which appear on the final invoice.
Once reconciled, transactions posted to the creditor cannot be changed or deleted without first deleting the reconciliation.