The data on which philosophical theorizing is based are rather the intuited contents themselves, concerning the various thought experiments. At least that is so outside the epistemology of the a priori.

A successful account enables us to understand human knowledge in general.

You attain aptness by judging while in good shape and in a good situation (good light, good distance, etc.), through the exercise of good barn-sorting epistemic competence.

We must distinguish judging from guessing.

Suppose we wonder whether we should trust the deliverances of our basic epistemic competences. If those are indeed our basic competences, then in order properly to satisfy our curiosity we will inevitably rely on one or more of them. So, either we squelch our curiosity or we will have to fall into the circularity or regress to which the skeptic objects.

There isn't a formal definition of success.

When there are conflicts of observation, when experiments cannot be replicated, scientists may then retreat to a study of the various specific observations so as to explain the conflict, in the course of which they would make use of the concept of observation, or of some specification of that concept.