Upon recalculation of the fuel after a ZFW drop your crit points are still good.
If after dispatch you are going to be less than required at the crit point after doing your own calculation are you going to divert or keep going?
Once in the air surely it does not really matter, you do what is required and often the airports used in the calculations are totally crazy. Who cares if you have fuel to fly over two suitable airports on the way to your crit point ERA after a depress.
If its good at the planning stage then really thats all you need.
Bet your an Aussie :-)