Linothorax vs Quilted linen vs spolas

[Dan Howard]

There are period references to Cordovan leather and implications that it makes superior armour but I was under the impression that nobody really knew what Cordovan leather actually was. Whether it was taken from a particular part of an animal or whether it was tanned differently. Is there a period source that tells us how Cordovan leather was made? I've seen speculation in modern texts but nothing to back it up.