Section 68
Assessment to be final and conclusive
Except as expressly provided in this Act, where —
(a)
no valid objection, petition for review or appeal has been lodged within the time limited by this Part against an assessment as regards the amount of the chargeable income assessed thereby;
(b)
the amount of the chargeable income has been agreed to under section 65(4); or
(c)
the amount of such chargeable income has been determined on objection, review or appeal, the assessment as made or agreed to or determined on review or appeal, as the case may be, shall be final and conclusive for all purposes of this Act and regards the amount of such chargeable income:
Provided that nothing in this Part shall prevent the Collector from making any refund under the provisions of section 77 or any assessment or additional assessment for any year of assessment which does not involve reopening any matter which has been determined on review or appeal for the year.