Where in the case of any proposal under section 69 of this Act—
(a) no notice of objection is served within the time limited by section 70(2) of this Act, or every such notice is unconditionally withdrawn; and
(b) either—
(i) the proposal was made by the valuation officer; or
(ii) the valuation officer is satisfied that the proposal is well-founded ; or
(iii) at the end of the period of four months beginning with the date on which the proposal was served on the valuation officer, that officer has not given a notice under section 74(1) of this Act,
the valuation officer shall cause the valuation list to be altered so as to give effect to the proposal.
Where the proposal was served on the valuation officer before the first anniversary of the coming into force of the valuation list to which the proposal relates, subsection (1)(6)(iii) of this section shall have effect as if for the words " four months " there were substituted the words " six months ".