Proving fraud
Based on the National Internal Revenue Code of 1997, the Bureau of Internal Revenue (BIR) has a period of three years after the last day prescribed by law for the filing of the return to assess internal-revenue taxes. Beyond this period, any assessment issued will be considered invalid. The exception is when there is a finding of fraud or falsity in the return filed or when no return was filed, in which case the applicable prescriptive period is 10 years.