SCO's fatal error?
By claiming copyright in the "Copyrighted Binary Interfaces" of C language header files, SCO is rendering its claim into the land of virtual fiction.
Header files do nothing except label things for compatibility through a system but as such they do not implment binary interfacing - they are ASCII files, not binary, and they only define common names between one useage and another.
In as much as the nuts and bolts of Unix are defined as a sequence of labels with values attached and that is a very generic definition indeed, is to say only that it is a computer language system. If some of the nouns or labels coincide that is due to a compatible operating system (note, it is not a binary compatible operating system, but object compatible) software may be developed with a "common binary interface". To claim that such as interface is unique is oxymoronic - it is a little like two countries that border over a river giving a bridge two different names.
Only, translattors are a bit of a nuisance in software - so a bunch of labels with names provides a common interface for reasons of planned compatibility.
It is a little like Noam Chomsky claiming copyright for "parts of speech".
It is not valid.