Service tax: where fraud-related notice fails, officer must assess tax for an eighteen-month period retrospectively. Where an appellate authority, tribunal or court concludes a proviso notice under sub-section (1) is not sustainable because charges of fraud, collusion, wilful mis-statement, suppression of facts, or contravention with intent to evade service tax are not established, the Central Excise Officer shall determine the service tax payable by that person for eighteen months, treating the case as if the notice were issued for offences subject to the eighteen-month limitation under sub-section (1).