I don't know if they are real supernatural prophecies, whether from God or the devil, or they are just kind of a folk tale that was passed down, or that cropped up at various times when people felt a need for it -- such as after the French Revolution, when Catholics dreamt of the return of the king. Or there could be a mix of real ones and fake ones, of course.
I would have to try to test each "prophecy" one by one, but I don't think I have enough information to do that. The best source I had was that book that was not Catholic; I should ask my priest if I can use that, as long as it shows no hostility to the faith. It appeared to be written in an objective style, but that can be deceiving.