"... delivered on time and within budget ..."

So for a project of this scale and timeline, they managed to use up exactly all the budget... (I assume it would say under/over budget if it was a significant amount off).

What are the odds of predicting correctly the cost of a 20 year project especially given the volatility of markets over the last 20 years?

I suspect either some corners were cut, or some contractors started padding out the bills towards the end...