Regarding "written by the hand of Abraham", I believe that Nibley claimed this meant that Abraham wrote the original, but this was a copy of a copy of a copy (ad infinitum) but by Egyption thinking could still qualify as "written by the hand of Abraham". This line of thinking addresses the fact that the document was written long after Abraham could have written it.
The proofs that are required in this day and age are indeed proof that the proven proofs are all we need to prove that the proofs which have given us the proof we need in order to demonstrate the proveable, are indeed proof. And unbelievably, there are still those who refuse to believe that which is believable only to believers who choose their beliefs based on belief in the believable.
And thus we see, that proof is only believable to believers in proof.