Fitz says he's making no allegation about Plame's status..and therefore need not and won't put in any evidence of that. Libby's lawyers are trying to make certain that Fitz doesn't try to sneak that in in a backhanded way--i.e., by suggesting as he has that thinking she was gave Libby a motive to lie.
Transcript of Special Counsel Fitzgerald's Press Conference
Valerie Wilson was a CIA officer. In July 2003, the fact that Valerie Wilson was a CIA officer was classified. Not only was it classified, but it was not widely known outside the intelligence community.