Owain Glyndwr: Thanks for the explanation. Yes, it was the Variable ZFW schedule that was used on the first half of the fleet until the higher gross weight fixed schedule aircraft became made available by Airbus. The later models had a 233tonne MTOW and 175tonne MZFW.
Would the wing structure have been "beefed up" or not considering that the A330 shared the much heavier A340's wing but with only two pylons? Or, would this have been a paperwork exercise?