161Period for which rent is not liable to modification.

Save as provided in section 163, when the rent of an occupancy, an exproprietary or a hereditary tenant has been commuted, abated or enhanced in accordance with the provisions of this Act, it shall not be liable to be commuted, abated or enhanced unless--
(i) in case of abatement or enhancement of rent--
(a) the revenue payable by the landlord has been revised; or
(b) there has occurred a decrease or increase in the productive power or the area of the land held by the tenant, as provided in clauses (b) and (c) of sections 153 and 154; or
(c) the sanctioned rates have been altered; and
(ii) in case of commutation of rent, a period of three years, or such longer period as may have been extended under section 83, has elapsed since the date of the last commutation order.