Can the AEC say with absolute certainty who has won a seat in order to declare the result without conducting a full distribution of preferences (DOP). This is possible either if the winner has a majority of the primary vote, or the second-ranked candidate has more votes than all other candidates combined.
If the second-ranked candidate has more votes than all other candidates, it is mathematically impossible for the third-ranked candidate (or another candidate) to overtake one of the top two, and thus you can be assured that the final two-candidate-preferred count tells us who has won.