Final classification order bars differential duty demand for the same period unless the earlier exemption decision is first challenged.

Differential duty could not be demanded for a period already covered by a final, unchallenged classification order granting exemption under Notification No. 52/86. The settled classification continued to govern that period, and the revenue could not reopen the same period's duty liability without first assailing the earlier order. Any fresh dispute, if maintainable at all, could arise only for a subsequent period. The operative effect was that the demand for the impugned period was unsustainable because finality had attached to the classification and exemption benefit.

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Issues: Whether differential duty could be demanded for the same period after the classification order granting the benefit of Notification No. 52/86 had attained finality and was not challenged by the department.

Analysis: The classification approved by the Assistant Commissioner in 1987 granted concessional duty benefit under Notification No. 52/86. That order was not challenged by the department and thus attained finality for the relevant period. Once the classification and exemption for that period had been settled and had become final, a later demand for differential duty for the same period could not be sustained without first assailing the earlier order. Any dispute, if maintainable, could arise only for a subsequent period.

Conclusion: The demand for the impugned period was not sustainable; the classification benefit under Notification No. 52/86 having attained finality, the revenue appeal failed.

Ratio Decidendi: A demand for duty for a period already covered by a final and unchallenged classification order granting exemption cannot be sustained without first challenging that order.

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