Work Practice for limit on cumulative duty time 60 hours in 168 hour period with at least 1 off duty period including 2 local nights

We are transitioning to CAO 48,1 on 1 Aug 2020. We have rosters which work to Appendix 4B para 7.1(b) If an FCM has had at least 1 off duty period of at least 36 hours, including 2 local nights during the period - 60 hours. However the only work practice set at the moment is 4B para 7.1(a) If an FCM has not had at least 1 off duty period of at least 36 hours including 2 local nights during the period - 40 hours. Our rosters will get a discretion at the end of their shift cycle (every 4 days) which will be very cumbersome when they are within the limits due to Appendix 4B 7.1(b).