To make sure the third sentence in paragraph 1.f. of the indictment was not easily shown to be untrue. Reporters would be nosing around Wilson's place after the indictment was handed down, and it would have been quite embarrassing if a reporter asked a neighbor, etc, ... you get the idea, it would be a fact automatically damaging to the prosecutor's credibility.
Fitzgerald gratuitously set-up the meme that Plame was covert, even to the point of putting the phrase "and her employment status was classified" in the indictment. All part of setting a misleading stage. But he had his case against Libby even without that misleading setting.
But when asked (I think it was one of the first questions), "So was she covert", he either said he didn't know or that was a question for the CIA. I have to watch the clip again. I remember my jaw hitting the ground and thinking even though it doesn't relate to this indictment, wouldn't that be the first thing you find out if you're to find out if her identity was leaked?