New Withholding Tax rates need to be applied retroactively- R12-12.1.3

Hello Expert,

I'd like to have your opinion/ consult in the following issue;

Our client has new Withholding tax codes that need to be applied retroactively as stated by the government!

- The Withholding tax is deducted upon the payment.

- The client already has old bugs in the withholding tax area since the upgrade time.

- the requirement is to apply the new codes for all the unpaid, partially paid and of course the new ones.

The unpaid and the partially paid are the challenging, as there are old invoices ( from 2:4 years ago) and potencially affected with the AWT bugs since the upgrade.