Despite sections 21 (1) and 22 (1) —
(a) if an appeal against, or review of, a decision on an objection to an assessment is started, the commissioner may, under section 17 , make a reassessment after the limitation period and before a decision is made on the appeal or review if the taxpayer agrees; and
(b) the limitation period does not apply to a reassessment made—(i) under section 18 (a) or 19 ; or(ii) under section 18 (b) if a provision of the revenue law for which the reassessment is made declares the limitation period does not apply.