A bit off thread but a colleague told me of a case recently. Taxpayer was owed a refund of tax for 2005 , they also owed Revenue a balance for 2004 and were further owed a refund of tax for 2009. The refund for 2005 was disallowed under the 4 year rule. The liability for 2004 ( also outside the 4 years but irrelevant ) was collected by reducing the 2009 refund and the taxpayer got the balance. Try explaining the logic of that to the taxpayer he said to me.