I would imagine that the 4 year rule will apply but dont take this is a definitive answer. If you were my client I would do some research to verify my answer. As an aside people and agents gave in too easy on these Revenue Investigations. The Revenue's tactics basically amount to bullying and intimidation. I had a client, a lady of 84 years who got such a letter. Due to health and memory problems she could not trace back to bank accounts where her savings were accumulated. The Revenue insisted on assessing her on the Capital despite the fact that she had worked for 70 years and lived a very simple life. The lady said that she would not allow herself to be bullied and we told the Revenue that they would not get a penny and that all monies on deposit were earned and subject to taxes despite us being unable to prove same. We invited them to assess her and insisted that we would appeal. The matter was dropped.