18 red empty seats? So you saying they leave these seats empty when there is 18 people wanting a economy seat?
Remember these seats are convertable seats which go from 2 seat a row to 3 seats a row. Just beacuse DJ don't sell the seats at Premium economy (W class) doesn't mean that they are not sold as economy (Y class) seats. If W sells it sells, if it doesn't, there is not stopping Y seats to be sold for a full Y class cabin.
As for the party, there are inecentives for the company to do it.
1. Morale - 5,000 people not bad for a party ( partners had to pay )
2. Tax and FBT laws allow it.
Frozen wages are for senior management.