How often do Z Classes run on Route 58?

Spotted Z3. 218 at the 58 terminus at Toorak earlier today; and I haven’t seen any other Z Classes on route 58 beforehand, so would this be a rare occurrence?

The wiki page does list Z, B and E Classes being used as well as the route being run out of Essendon and Southbank; so maybe the AO is using more of the E Classes hence the Z filling in?