#1. It doesn't matter whether there was an earlier letter. Comey was the "Acting Attorney General", like it or not. This was the grant of authority under which Fitzgerald was acting throughout most of his investigation and at the time of the indictment.
#2. Even under the first letter, Fitzgerald was granted the power of the Attorney General for the purpose of investigating the alleged unauthorized disclosure. The second letter appears to be only a clarification, probably requested by nit-picker Fitzgerald.
#3. Valerie Plame was, in fact, a covert agent. Those claiming otherwise are misinforming the American public. The definition of "covert agent" is from the subchapter of the US Code that contains the IIPA and Valerie Plame satisfies that definition. She had indeed served abroad as a covert agent within the last five years.
#4. There is also the 1917 Espionage Act to consider, which makes it a crime to disseminate classified information.
Wotan, I respect your perspicacity, truly. But...
The original order from Comey to Fitzgerald was very, very narrow and limited to investigating only 2 things-
whether there was a violation of Title 50, US Code, Section 421 (Disclosure of the id of covert intel personnel) and Title 18, US Code, Section 793 (improper, "unauthorized" disclosure).
I admit that, yes, Fitz DID have the auth, from Comey, to expand his investigation into the 5 resulting counts of indictment (restricted to "Obstruction of Justice", "False Statements", and "Perjury") but SOMEONE should look into WHY and on what grounds could he go fishing any further, after he found that no underlying crime (the 2 Codes specified, above) occurred. It would be sorta like investigating Fitz' motives, even though he perhaps committed no crime,sorta like he did to Libby. If this had happened in a state GJ proceeding, the supervising judge would've (unless he was a crypto-Dem) stopped it, b/c it would've been challenged as "bad faith" on the part of the prosecutor. But this was a Federal GJ, and so we see this batch of perjury traps- highly indicative of Fitz' motives? This is why so many ham sandwiches are indictable-no supervision of Federal prosecutors. Pretty scary in a democracy.
Further, according to Andrew C. McCarthy (NRO), Bill Girtz (WashP), and the amici curiae (NBC, CBS, NYT, WashP, et al): there was no standing for the GJ b/c Plame was no covert agent within the 5-year period, b/c she had been outed twice before that! So, the press did know who she was?!
What I'd really like to know is: why do you say Plame was a covert agent in the 5 years preceeding (July 14, 2003)? Doesn't the fact of her having been outed (by the Ruskies and then, "inadvertantly"? by the CIA, in Cuba) nullify any later "covert" status? And let's not forget that Libby may yet claim he was, indeed, authorized.