193.1.Alterations made under section 193 have effect as follows:
(1) every alteration contemplated in subparagraph 1 of the said section has effect in respect of the fiscal period during which it is made and in respect of the previous fiscal period if the roll in force for that year contained the same error;
(2) every alteration contemplated in subparagraph 2 of the said section has effect from the date fixed in the assessor’s certificate, which date may not be prior to the more recent of the following dates:
(a) the date on which the event justifying the alteration occurred;
(b) the date of the first day of the fiscal period preceding that during which the alteration is made.