12Where after the date on which the control order comes into force—
(a)the valuation list is altered so as to vary the gross value (or where paragraph 11 applies the net annual value) of the house or of the hereditament of which the house forms part, and
(b)the alteration has effect from a date before, or from the same date as, the control order came into force,
compensation is payable as if the value shown in the list on the date when the control order came into force had been that shown in the list as altered.