Differences between nominal & backdated debtors/creditors list is likely caused by a timing issue between the processing date and transaction date.
The back dated reports take into account items that may have been physically posted within Navigator and back into the period. The report doesn't back date 100%.
Ideally the report needs to be taken off of the system on the last day of the year. As it is at it's most accurate at this point.
To provide what the differences are you can run a Scheduled Nominal Report and Back Debtors/Creditors report and match balances off, this way you can identify which accounts have differences quickly.
You can then review the accounts and check the date the transaction has been processed, this will show it is after the transaction date. Most Auditors will be happy as the dates when the transaction were posted are audited fully..