"At first I thought, well he never experienced a god, so how could he say he knows of them from prolepsis."
This sounds to me as though you are not considering a prolepsis to be an experience. That's an issue we talk about regularly without much to work with, but at the very least: To the extent that prolepsis processes not only the five senses but also the feelings and also "images," I think some would maintain that Epicurus regarded "knowing them from prolepsis" as indeed "experiencing" them.
Bryan would you say that differently?