In August, Cohen pleaded guilty as part of a separate investigation by the Manhattan US attorney's office, and he has since given over 70 hours of voluntary interviews to the special counsel.
Mueller's office says Flynn assisted them 'on a range of issues, including interactions between individuals in the Presidential Transition Team and Russian Federation'.
The memo said prosecutors can't reveal the extent of his cooperation because "the investigations in which he has provided assistance are ongoing".
Prosecutors said Flynn's "record of military and public service" set him apart "from every other person who has been charged" in Mr Mueller's investigation. However, senior government leaders should be held to the highest standards.
Mueller's team is looking into whether Stone, an informal adviser to Trump during the 2016 campaign, was in communication with WikiLeaks before the website publicized stolen emails from Hillary Clinton's presidential campaign. CNN's Manu Raju observed that Trump is offering a "big signal here" that he could pardon Stone and is "encouraging him not to cooperate".
The memo is due today for Flynn, who pleaded guilty more than a year ago to lying to the Federal Bureau of Investigation about speaking to Russian officials on Trump's behalf. Flynn later pleaded guilty to perjury and is cooperating with Mueller.
Mueller had to file his recommendation for sentence before a midnight deadline on Tuesday. Flynn was under investigation by the Justice Department for that work when he became national security adviser.
Federal sentencing guidelines recommend between zero and six months in prison for Flynn, leaving open the possibility of probation. According to the addendum, Flynn has assisted with two other matters - at least one of them a criminal investigation - besides Mueller's Russian Federation probe, but those other matters are redacted.
Flynn also admitted to lying on his foreign lobbying registrations about his lobbying in Turkey.
But for the most part, prosecutors will spell out in detail the matters they believe the former Trump campaign chairman misled them about, and their public disclosures could shed new light on where the Russian Federation investigation stands.
Trump has long surrounded himself with liars, and for quite a while he's been using Twitter to praise the liars who impede the Mueller probe and castigate any former confidante who agrees to tell Mueller the truth about Trumpworld.
Last week, Corsi refused Mueller's offer for a plea deal over his role as a suspected intermediary between Stone and WikiLeaks, saying he was prepared to spend the "rest of my life" in prison rather than "sign a lie".