In a common PIOsolver analysis of a hand, we typically assume that players are playing according to GTO ranges preflop. Suppose we make this assumption and then play optimally according to the solver's solution. Would that mean that our strategy is unexploitable for the whole game tree? Or is it possible that players can exploit us by changing their preflop strategy and therefore invalidating our range assumptions?

In other words: Is solving a postflop spot with the assumption of GTO preflop ranges equivalent to solving the entire game tree from scratch, including all preflop play?