(1) This section operates if the group came into existence during the period to which a group liability relates.
(2) The contributing members' liability under subsection 721 - 15(1) to pay the group liability is limited to the proportion of the group liability that is reasonably attributable to the period:
(a) beginning at the time the group came into existence; and
(b) ending at the time when the period to which the group liability relates ends.