It wasn't much of a “knock out” since I have had the chemistry, organic chemistry, biochemistry, and genetics courses ( both on the undergrad and grad school level) to fully understand the article.
However...the author states:
“Now, it would not be fair, just because we have presented a realistic evolutionary scheme, supported by gene sequences from modern organisms, to suggest that we now know exactly how the clotting system has evolved. That would be making far too much of our limited ability to reconstruct the details of the past. But nonetheless, there is little doubt that we do know enough to develop a plausible and scientifically valid scenario for how it might have evolved. And that scenario makes specific predictions that can be tested and verified against the evidence.”
Well yeah, as with anything that involves the universe before humans started taking notes it’s unobserved and therefore we’re guessing based on trace evidence and logic. Until somebody invents a time machine we’re kind of stuck with that for astronomy, planetary sciences, geology, anthropology, paleontology, evolutionary science and a bunch of others.