On what basis can we evaluate claimed revelations (such as the Bible or the Qur'an) as divine in origin?

On no basis whatsoever.

Secondarily, it's all babble.

If IFs bred like rabbits, we'd be up past our necks in maybes. But hypothetically, did you ever play "telephone" with a bunch of people? You know, where the first person thinks of a sentence and whispers it on to the next person. If the particpating group is big enough, you could have the sentence "time flies like an arrow" get to the last person as "clock insects enjoy a weapon."

Nor is there a single date when we can say that the canon of the New Testament was decided. In the first and second centuries after Christ, many, many writings and epistles were circulating among the Christians. Some of the churches were using books and letters in their services that were definitely spurious. Gradually the need to have a definite list of the inspired Scriptures became apparent. Heretical movements were rising, each one choosing its own selected Scriptures, including such documents as the Gospel of Thomas, the Shepherd of Hermas, the Apocalypse of Peter, and the Epistle of Barnabas.

Gradually it became clear which works were truly genuine and which mixed truth with fantasy. By the end of the fourth century the canon was definitively settled and accepted. In this process Christians recognize the providence of God in providing us with his written revelation of himself and his purpose with the universe.

Questions still arise now and then about the canon. Some wonder why just these 66 booklets were chosen. Why not 65 or 67? Why was the sometimes puzzling booklet of Jude included to the exclusion of other edifying scriptures? To these questions we reply that these books are the ones that God himself has chosen to preserve for us, and he has not told us exactly why. Together they form an immeasurable treasure, and in them we find God's matchless gift to his people. Here we are moved simply to trust in his providence as he led his people through the years and gave us the most honored and powerful and comforting volume in the history of humanity, the book known as the Bible.