The assessable income for the * current year of a company that is not required by law to insure, and does not insure, against liability for workers' compensation claims includes an amount equal to the amount (if any) by which:
(a) the value, at the end of the previous income year, of the company's liability for such claims that:
(i) arose from events that occurred in that or an earlier income year; and
(ii) were not paid in full before the end of the previous income year; exceeds
(b) the value, at the end of the current year, of that liability.
Note: Those values are worked out under section 321 - 90.