I have absolutely no problem with including the headers
inside the message. Indeed, if you want to provide some
degree of assurance as to who was at least _supposed_
to have been copied, this is a reasonable approach.
(Note that it doesn't prove that you actually _did_ copy
those individuals, however.)
But unless you embody that informatin in a particular
MIME format, it is just text, and could just have well
been indiciated in a cc list.
I think the issue is wherther you should be able
to _count_ on these headers being there, and for
now, at least, the asnwer is presumably no.
Bob