Limitation on service tax demands governs validity of show cause notices and enables specified recovery remedies. Section 73 permits recovery where service tax is unpaid, short paid, short levied or erroneously refunded and generally requires issuance of a show cause notice within prescribed limitation periods computed from the relevant date. Extended limitation applies for fraud, collusion, wilful mis statement, suppression of facts or intent to evade; otherwise a normal thirty month period applies. Self assessed but unpaid tax declared in a return may be recovered without a notice under the recovery modes specified in Section 87, which include adjustment, garnishee proceedings, distraint and recovery as an arrear of land revenue.