We are faced with complex questions of facts and our own interpretations of those facts. This always boils down to credibility, the final analysis, a theory that can actually include a perception of those ancient reports in their own language capacities.
The principle with comparative studies is that interpretations begin with what the cultures themselves flatly state or claim. Because we have broad parallelism of symbols and symbolic themes among ancient cultures - as people like Jung noticed - we also have the ability to test what one culture asserts about a symbolic element against how other ancient cultures understood the same element, and essentially triangulate on confirmation of a viewpoint. Beyond that we have some interesting facets of ancient symbolic language that point us to specific nuances of meaning.