Section 30

Except as expressly provided in this Act, where no valid objection or appeal has been lodged within the time limited by this Part against an assessment as regards the amount of the chargeable tax assessed thereby or where the amount of the chargeable tax has been agreed to under section 26(4), or where the amount of such chargeable tax has been determined on objection or appeal, the assessment as made or agreed to or determined on appeal, as the case may be, shall be final and conclusive for all purposes of this Act as regards the amount of such chargeable tax:

Provided that nothing in this Part shall prevent the Collector from making any refund under the provisions of section 36 or any assessment which does not involve re-opening any matter which has been determined on appeal for the year of assessment.