The previously attributed GST amount for a supply is:
(a) the amount of any GST that was attributable to a tax period in respect of the supply; plus
(b) the sum of any * increasing adjustments, under this Subdivision or Division 21, that were previously attributable to a tax period in respect of the supply; minus
(c) the sum of any * decreasing adjustments, under this Subdivision or Division 21 or 134, that were previously attributable to a tax period in respect of the supply.