I view the value of the Bible in a different way than your question presupposes, but that shouldn't matter as far as the nature of the claim I made and the point I have in making it and asking him to substantiate his opposition to it. The reason I say that is because the idea of fulfilled prophecy, in the sense of prediction of the future, is a reasonably objective claim. It's not a matter of purely subjective opinion, there are reasonable standards about what would count as a successful prediction.
In fact, the entire point of this argument from prophecy that sassyam is making is that prediction of the future is difficult. So much so that, according to sassyam, even one fulfilled prediction would establish the supernatural authority of the biblical texts. It's a rational and objective argument, and so it should be evaluated in a rational and objective way. If the argument can't be reasonably established, then the claim to authority fails. My opinion is that the argument does, very clearly, fail, and so a different model of the "authority" or value of the biblical text is needed. I don't see how, even as a Christian, it would do any good to deny the clear and rational failure of the argument. I believe that Christians may plausibly make an argument that an authentic understanding of Christianity accepts the reality of things which transcend pure rationality, and yet it makes no sense to willingly fall into irrationality, especially while relying on ostensibly rational arguments to substantiate claims to authority.
This isn't a prediction of the future, but it also doesn't count as knowledge that we would be surprised that ancient people had. It is a matter of empirical observation: if you drain the blood out of animals and people, they die. Ancient people lived very close to nature. It's not surprising that basic physiological facts didn't escape them. To give another example, in an ancient hymn of the Rg Veda, it is asked "Where is the blood of earth, the life, the spirit?" (Rg Veda 1.164) The question there (and in the greater context) certainly implies an understanding that blood is central to life. Ancient hebrews were not alone in that understanding.