The provision of twenty (20) sick leave teaching days in any Institute year shall be prorated in the following circumstances:
(a) Where a teacher commences employment at a time other than the commencement of the Institute year.
(b) Where a teacher returns from a leave at a time other than the commencement of the Institute year.
(c) Where a teacher terminates employment during the Institute year for reasons other than sickness.
(d) Where a teacher commences an unpaid leave of absence for reasons other than sickness.