A year after being fired by former Trump national security adviser Michael Flynn, lawyers at Covington & Burling revealed Thursday that they recently uncovered emails and handwritten notes that were "inadvertently" left out of a trove of records turned over last summer to his new defense counsel.

In a court filing, Flynn's former lawyers at Covington said they had discovered the records as they prepared to respond to the retired Army general's allegation that the firm provided him with ineffective counsel. Flynn has criticized Covington's representation of him amid his bid to withdraw his 2017 guilty plea, in which he admitted to lying to the FBI about his past communications with the Russian ambassador to the U.S.

The law firm said it had turned over the newly uncovered emails and two pages of handwritten notes Thursday to Flynn's lawyer, Sidney Powell, who was hired in June 2019 after the former Trump adviser fired Covington partners Robert Kelner and Stephen Anthony.

"With respect to the emails, this appears to have resulted from errors in the process of collecting and searching electronic materials that were not contained in the working case file. The two pages of notes appear to have been inadvertently missed during the file transfer process," Kelner and Anthony said in Thursday's filing.

The lawyers raised the possibility that Covington had missed other records last year as it handed the Flynn case over to Powell, a former federal prosecutor who gained notoriety in conservative circles for railing against the Russia investigation on Fox News.

"We are in the process of working with our information technology personnel, as expeditiously as possible, to determine what other materials were not captured by the prior electronic searches and to collect and transfer them promptly to Mr. Flynn's current counsel," Kelner and Anthony said. "We will apprise the court when this is completed and will provide any further information that the court requires."

A Covington spokesperson declined to comment on the firm's filing Thursday.

In a July court filing, Covington lawyers said they "take very seriously the obligation to protect the interests of a client in connection with any termination of a representation."

Flynn's sentencing, originally set for December 2018, has been delayed for months as a federal judge in Washington weighs whether to allow Flynn to withdraw his guilty plea. Prosecutors in recent weeks have suggested that Flynn be sentenced to up to six months in prison, after previously backing his request for probation.

Reached for comment Thursday, Powell said "Covington's new find of documents is very interesting on many levels."

"Stay tuned," she said, calling Flynn's prosecution a "travesty from every angle" and accusing the government of withholding critical documents. Prosecutors have disputed that they kept any information hidden from Flynn.

"This case was manufactured from its inception and evidences the DOJ and FBI at their worst," she added. "The longer the DOJ takes to dismiss this persecution, the less credibility it has."

Since replacing his Covington defense team with Powell, Flynn has spent months assailing his former lawyers while also accusing the Justice Department of prosecutorial misconduct. In December, the federal judge overseeing Flynn's case rejected Powell's claims that prosecutors withheld favorable evidence from Flynn and entrapped him in an interview concerning his contacts with Sergey Kislyak, the former Russian ambassador to the U.S., in the time between Trump's election and inauguration.

"The court summarily disposes of Mr. Flynn's arguments that the FBI conducted an ambush interview for the purpose of trapping him into making false statements and that the government pressured him to enter a guilty plea," U.S. District Judge Emmet Sullivan of the District of Columbia wrote in his ruling. "The record proves otherwise."

Meanwhile, Covington remained largely silent in the face of Flynn's criticism, citing bar rules and legal ethics norms that require lawyers to preserve a tight seal around the confidences of former clients. But in early March, at the urging of the Justice Department, Sullivan issued an order freeing Covington to respond to Flynn's claims of ineffective counsel.

Covington combed through its files in response to that order. In August, Powell said the firm had provided her with "more than 300,000 documents."