[notreallyhere00]

Appeal to authority is only a fallacy when the authority is not an actual authority on the exact topic being mentioned.

Your broader point is right; obviously if we stop to poke at certain assumptions, the occasional one will collapse.

However, the pathway you’ve just suggested is less practical than you think. The GP is talking about a systematic, coordinated exploration effort of known unknowns.

Metaphorically - he/she is saying that there’s more likely to be gold at the unexplored end of gold mine, not in the excavated dirt.

It’s a fair assumption to keep in practise.