There's nothing special about "these things", but in general I'd stipulate (and if I need to take this axiom than so be it) that any possible world which allows a human being to communicate information with another intelligence through some symbolic medium under a consistent history also allows for the possibility that this experience could be counterfeited (by either the intelligence itself, flaws in the human's abilities, or a malicious third party) at a non-zero probability.

Of course, I think at this point I'd also be willing to amend my original declaration to "a human being can 'almost never' update on an initial probability assignment of zero", and leave the dissection of this "sheer coincidence" to more interested parties.