(1) If the income that a bankrupt is likely to derive, or derived, during a contribution assessment period as assessed by the trustee under a subsequent assessment exceeds the actual income threshold amount applicable in relation to the bankrupt when the subsequent assessment is made, the bankrupt is liable to pay to the trustee a contribution in respect of that period.
(2) The liability of the bankrupt under subsection (1) in respect of a contribution assessment period is in substitution for any liability of the bankrupt in respect of that period under subsection 139P(1) or under any previous application of subsection (1) of this section and has effect despite subsection 139P(2).
(3) If the income that a bankrupt is likely to derive, or derived, during a contribution assessment period as assessed by the trustee under a subsequent assessment does not exceed the actual income threshold amount applicable in relation to the bankrupt when the subsequent assessment is made:
(a) the bankrupt is not liable to, but may if he or she so wishes, pay to the trustee a contribution in respect of that income; and
(b) any liability that the bankrupt had under subsection 139P(1) or under subsection (1) of this section to pay a contribution in respect of that period is extinguished.