Also, I think we can consider that concepts like "good," or "the good" or "the highest good" or "pleasure" (when viewed as a concept) or " the highest pleasure," or "gods" are, like virtue, good examples of the issue.
Determining what these things at the start of our quest is not an easy thing. People disagree on what those words mean, and it is exactly the definition of them that we don't have as a test. How will we know we are correct when we assert that "x" or "definition X" of the highest good is correct? Same with "absence of pain." If we knew we wouldn't have to ask, and if we don't know then how do we know when we have arrived at the correct definition?
One way to do it is to use our experience of "images" we have received in the past as the basis for extending out a definition. We can suggest formulations such as "a god is a living being blessed and imperishable" or "pleasure is the absence of pain," because these are reaonable extensions of more limited past experiences. Once extended as a formulation, we can then test those extensions logically against more actual experiences to confirm or contradict that formulation as a workable definition. But where did the proposed definition come from in the first place? From "extending out" descriptions of actual experiences received as images, either in our own past after birth or encoded in rudimentary fashion genetically before birth from past generations.
Experiencing men six feet tall and living 60 years allows us to conceive of the possibility of men 60 feet tall and living 600 years, even if we have never seen such ourselves. We have seen some men spend more of their time living pleasurably than others, so we can conceive of living beings who spend *all* their time living pleasurably.
But we cannot even conceive of anything coming from nothing because we have logically concluded based on much experience that this is not possible at all. And we cannot logically conceive of a totally happy being finding itself in a situation where its total happiness is interrupted by getting mad at enemies or feeling any lack to be filled by "rewarding" friends.
It's not necessarily supernatural to live 100 years or 600 years, but it would be supernatural to create anything from nothing, or to create the universe as a whole from scratch, or for the universe to have an end in space, or for a spirit to exist apart from a living body.
I presume Epicurus would point to prolepsis and your explanation of a sequence in which it would work as a much better approach than "recollection of knowledge from before birth" or "it's impossible to know anything so let's admit we know nothing," or "let's talk about it using the dialectical method."
Appealing to Prolepsis along the lines you describe (plus making clear that "images" are not limited to "visible images") gives us an approach that allows us to be confident of basic conclusions where evidence is strong. It also gives us a workable test to determine when evidence is insufficient, requiring us to "wait" before being confident a single opinion is true.
As Lucretius wrote, even the gods could not conceive of creating a universe if they had never previously received an image of a universe, therefore the gods could not predate and be the creator of the universe. But even we as humans can conceive of terraforming Mars, because that idea is a reasonable extension of images we have in fact received in human experience reshaping things here on Earth.
