The "establishment" sources can be used in anti-establishment ways. Carlo Ginzburg does this ingeniously in his books. Obviously the witch- and heretic-hunters were looking for a hierarchical cult of Satan-worshippers (and the present-day neopagans are after the same thing with an inverted value system) - but the trial evidence they wrote down told a very different story, which Ginzburg traces explicitly over a very long route in space and time (some of it paralleling what Lloyd wrote about The Outlandish Knight). The trick is to look at the stuff the witch-hunters wrote down when reporting interrogations and confessions but couldn't make sense of within their dualistic framework.

But the story is about folk beliefs clustering in different ways in different contexts, not a doctrinal history of a unified anti-Christian religion.