I think conservative companies have far more room for technical...

I think conservative companies have far more room for technical errors and financial errors.
There are many assumptions made when modeling these projects such as flows, seepage, rates of evaporation, recoveries etc.
Conservative companies allow more margin for error.
Other factors provide for margins of error such as high grade, high evaporation, lined ponds, high flow rates, big resources.
Conservative companies are less inclined to assume high SOP prices or low exchange rates or get into risky debt situations. They will include large contingencies and pre-production working capital in their feasibility. Conservative companies get all their ducks lined up.

So imo its more than just technical in house expertise.