Steve
I have not looked into it carefully, but have had two excellent archivists indicate that there may be some doubt as to their being Confederate in origin - or at least that it is yet to be determined with certainty. The NARA Z33 portfolio listing, however, clearly indicates that they are captured Confederate maps. I was told once (but I have forgotten by whom) that Gary Joiner had doubts, but I have not asked him directly about the Z33 portfolio provenance.
Don