GUANTÁNAMO BAY, Cuba — Prosecutors volunteered on Friday to review hundreds, perhaps thousands, of pages of classified C.I.A. documents in the Sept. 11 case to determine if some material provided to defense lawyers was too heavily redacted.

The acknowledgment that some secrets at the Guantánamo court may no longer be secret came on the fourth day of a hearing in the complex conspiracy case against Khalid Shaikh Mohammed and four other men who are accused of plotting the hijackings that killed nearly 3,000 people on Sept. 11, 2001. The capital case has been in pretrial hearings since 2012, one reason information once considered national security secrets may now be made public.

In a presentation, James G. Connell III, a defense lawyer for Mr. Mohammed’s nephew, Ammar al-Baluchi, told the court that he had so far obtained 1,025 pages of once classified cables and other documents from the C.I.A. through the Freedom of Information Act, which included more details than prosecutors and the judge had approved for use at the eventual death-penalty trial. The agency is preparing to release another 2,100 pages of secret documents, Mr. Connell said.

Mr. Connell offered as an example a May 3, 2003, report from a C.I.A. black site prison on an interrogation of Mr. Baluchi, probably in Pakistan, that the agency released through the Freedom of Information Act.

The prosecution version, invoking a national security privilege, covered up the day of the month as part of a routine practice by prosecutors of blurring dates of C.I.A. reports from the black sites; omitted the title “Ammar al Baluchi Interview” and certain tracking information; and redacted parts of sentences showing the source of certain information was Majid Khan, another black site prisoner, who recently said in court that he made up lies while being tortured to satisfy his interrogators.

A lead prosecutor, Clayton G. Trivett Jr., agreed to the review, saying that “there is some reconciliation that needs to be done” by his team. He said prosecutors would compare documents released by the C.I.A. under FOIA to those his team had prepared and given to defense lawyers.

Mr. Trivett said that if the C.I.A. has subsequently changed its theories or rules of classification, “it cannot be” that “the public” has access to more complete documents than defense lawyers and, potentially, ultimately a jury get.

Mr. Mohammed and the other defendants were captured in Pakistan in 2002 and 2003. The case is mired in hearings on whether admissions they made to F.B.I. agents after their arrival in Guantánamo in 2007 were tainted by their torture.

The new judge, Col. Matthew N. McCall of the Air Force, is hearing dozens of pleadings by defense lawyers who want the court to order the government to search for and turn over information they argue may be missing from the first six or seven years of the accused plotters’ detention.

It was unclear how much time the prosecution’s review would take, or whether it would further set back efforts by prosecutors to bring the case to trial. Mr. Trivett also did not appear to commit to review all the classified documents in the case.

But the development underscored how the landscape of public information has changed in the nearly 10 years that the case has been in pretrial proceedings, particularly through litigation in other courts and through government leaks.

Just last month, when the Supreme Court wrestled with national security invocations in a civil case involving claims of torture of a Guantánamo prisoner, Abu Zubaydah, at an overseas C.I.A. prison, several justices openly named the country in question as Poland.

“The fact that he was tortured by these contractors in Poland, that’s not a state secret?” Justice Amy Coney Barrett asked in a question that, under current rules at the court at Guantánamo Bay, would have constituted a spill of classified information.

To prevent such information from reaching the public from the Guantánamo proceedings, the Pentagon court has a 40-second delay on audio broadcast into the spectator’s gallery, time for a security officer inside the court to mute what the public hears.

Prosecutors have consistently invoked the national security privilege for the names of every country that hosted a black site in the C.I.A. program, which was established in 2002 and was closed in 2009, because the nations that permitted the United States to run the secret prisoners were promised anonymity. Permitting the site to be mentioned, the explanation goes, would harm foreign relations.

Two years ago, prosecutors were forced to revisit their classification decisions in Guantánamo’s other death-penalty case after the Army judge there ruled that their deletions “could fairly be characterized as self-serving and calculated to avoid embarrassment,” and “indicative of a minimalist view” of evidence defense lawyers were entitled to receive.

Mr. Trivett, a lead prosecutor in the Sept. 11 case, committed his team to conducting the review soon after Mr. Connell’s presentation, rather than wait for the judge’s ruling on the question.