Is there any reason (or truth for that matter) in the KE having a higher stated fuel consumption than newer third gen models?

Lack of egr?

There were changes to Australian standards in measurements of fuel efficiency (in 2001) and it was measured in a different way to which they had previously.
As per usual in a protected industry, the aus manuf. were probably given some to improve there intended ratings before the new systems was introduced.
Many cars were now rated lower than they were previously.

I'm not how much impact, if any, this had on the your question about Efficiencies of your model, but I suspect it may be somewhere near the truth to answering your question.

The newer models used transmissions with higher gearing to lower engine revs when cruising. Also the INVECS programming seems to have been changed to make the transmission go into a higher gear more often and not change down automatically when going down a hill.