Update 5:06 P.M.: A State Department official told the Free Beacon that the November 2014 date in the court filing was an administrative error. The State Department said it first received the document in June 2015, and disclosed the decision to withhold in July 2015. The department said it would be filing a correction.

"The State Department generally does not comment on matters in litigation," said a State Department official. "Here, however, there is confusion arising from an administrative error in recent correspondence in which the Department said that the document in question was withheld in November 2014. That is incorrect. The complete facts surrounding this document are set forth in a public court filing from July 2015. As described in the attached filing, the Department received the document in June 2015 from members of former Secretary Clinton’s senior staff, and did not withhold it until that time. The Department regrets any confusion and will be sending corrected correspondence to Judicial Watch."

UPDATE 6:05 P.M.: Judicial Watch called the State Department's response "another misleading statement from the Obama State Department," and said the department has given changing dates for when it discovered the document in question.

"These ever-changing stories and excuses are exactly why Judicial Watch was granted discovery into these issues by two federal court judges," said Judicial Watch President Tom Fitton in a statement to the Free Beacon.

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A watchdog group said on Tuesday that the State Department withheld a document that would have revealed Hillary Clinton’s use of a private email address two years ago, before finally agreeing to release it earlier this month.

The Sept. 29, 2012, document, an email to Clinton from her Deputy Chief of Staff Jake Sullivan, included Clinton’s private email address. The email discussed talking points related to the Benghazi attack.

Judicial Watch, a government watchdog group that has been suing the State Department for Clinton’s records, said the State Department first agreed to partially release the document in an April 18 court filing. Attorneys for the State Department said the email was initially withheld from Judicial Watch, as noted in the department’s Nov. 12, 2014 letter to the watchdog group.

But Judicial Watch said the November 2014 letter did not mention that any emails had been withheld. The group said the existence of the email was noted in a search declaration from the State Department, which indicated it was first discovered in September 2014.

Judicial Watch criticized the delayed release on Tuesday, saying "Clinton’s email server and her hidden emails would have been disclosed nearly two years ago, before Clinton authorized the alleged deletion of tens of thousands emails" if the State Department had turned over the document earlier.

"Now we know the Obama administration consciously refused to give up key information about Hillary Clinton’s email in 2014. It covered up this email both from the court and Judicial Watch," said Judicial Watch president Tom Fitton in a statement on Tuesday. "Judge Lamberth was right when he suggested that Obama’s State Department acted in bad faith. This cover-up provided Hillary Clinton enough time to hide potentially thousands of government records. One aim of our court-order discovery will be to get to the bottom of this cover-up."

The revelation that Clinton used a personal email address—which was first revealed by hacker Guccifer in 2013—would not necessarily demonstrate that she was using a private, "homebrew" server. However, the State Department’s decision to withhold the email for two years reinforces the claim from critics that it has not been completely transparent in the public records process.

The State Department did not respond to request for comment by publication time, but this story will be updated with any comment.

The Washington Free Beacon reported last week that State Department officials transferred and "retired" files from the executive secretary’s office to another bureau after receiving a subpoena from the House Select Committee on Benghazi last April. The Benghazi-related documents were rediscovered by the State Department’s public records office last December.

The decision to transfer the files, which included electronic folders used by senior State Department officials, significantly delayed the release of the documents to Congress.