"I hereby affirm that my prophecy will be correct, JFK will be shot dead near the end of the 60s in Dallas. Cheers, Dixon, 5 May, 1958."
Technically, that would be an incorrect prophecy, since JFK was killed in 1963.
But I see what you are getting at.
I only claim I would then believe (with high certainty) that note was written after Kennedy was killed and it would still take quite a bit of evidence to convince me it was written before JFK was shot. Do you think that is the wrong conclusion to draw?
I suppose I could see why you would accept that as a prima facie conclusion. What I think bothers me about the statement is the phrase "with high certainty." The problem, again, comes down to the question of whether one accepts that prophecy is a real possibility. You've said that you acknowledge that as being so. If that is the case, why necessarily conclude in an a priori fashion that the prediction almost certainly could not have occurred as claimed? If there really is no anti-prophecy bias at work, then the information should be evaluated as to its claims, not dismissed as being highly improbable.
Suppose in this scenario, Dixon had accumulated a group of followers prior to 1963 who touted the possibility of a president being shot dead in Dallas at that time? What if these followers believed in Dixon's prophecy so strongly that they were willing to undergo personal hardship or even death in order to spread her message far and wide - a message that, if it was false, they were in a position to know was false? Suppose, further, that the government considered these followers to be a problem and so began to suppress them, even violently? Would things like this happening before 1963 change your view of the possibility of the prediction being a real prophecy?
Are you saying unicorn and fairies are a-priori impossible but the existence of god, angels etc. is not?
No, that's not where I was going with that at all. I was trying to gague your openness to actual prophecy by seeing whether you would put real prophecy in the same basket with things like fairies and unicorns, or whether you actually considered it a real possibility.
And of course, your remarks about unicorns are correct; some might even use the term of a rhinoceros.