The differences are probably in the details of the PEA. Its unusual to straight line project revenues and costs when doing a NPV when both are expected to change over time. In certain years planned production levels, recoveries, prices, head grades, capital costs, etc will vary. Trying to duplicate the summary information that has been published without the PEA input details is admirable but next to impossible. I'm inclinded to give the pros the benefit of the doubt that they did it right.

... Been There