If they use $1750 again, it might make NPV fall due to high...

If they use $1750 again, it might make NPV fall due to high inflation in CAPEX and OPEX, but no change in predicted gold price. What was the spot price when $1750 was used? $1855 spot price today. So they should still pick the 'most correct' forward gold price.

The SS2 would likely include a sensitivities analysis to be able to equalise for gold price anyway, if wanting to compare the 2 studies.

Eg. if SS1 had used $1850 gold price instead of $1750, it would have showed US$513m or so NPV instead of US$381m (I calculated based on the below chart).