I didn't think you could do overtime on an annual leave day. If there was a regular need to find extra staff because there was too much work, they could just cancel the program. If they sack the blokes and there is nobody to call back, they have no alternatives.
Variants of this program would run constantly. The ones in this presentation generally consume about 4 weeks of annual leave to run and would, subject to who is transferring to Perth or Bne, mean that nobody would get CR.
By burning an extra 4 weeks each year, most sections could run at those staffing levels for about 10 years before all leave was consumed. By then half the blokes would have retired anyway so as each person retires, the need to burn leave reduces. Remember the average age now is about 53.