Yeh plenty of occasions where they use discretion. E.g. company about to bought out, etc. No point rebalancing.
If you look at Fairfax they listed Domain Group, so thats an "extra" company. But at the same time Tatts/Tabcorp going through a merger.
In any event they will need to make room for A2M shortly. Curently sitting at $5.2B Market Cap.