(1) A * decreasing adjustment under this Division is attributable to:
(a) the same tax period as the * taxable supply to which it relates; or
(b) if it relates to a supply that is not a taxable supply--the tax period to which the supply would be attributable if it were a taxable supply.
(2) This section has effect despite section 29 - 20 (which is about attributing your adjustments).