Nevertheless, cooperating witnesses who pleaded guilty are not usually filing Brady motions. When a defendant cuts a deal with prosecutors, his sentence depends greatly on how the prosecutors view his cooperation. Moreover, in his plea, Flynn agreed to “forego the right to any further discovery or disclosures of information not already provided at the time of the entry of Flynn’s guilty plea.”
http://thehill.com/opinion/judiciary/374738-evidence-withheld-in-flynn-case-brady-motion-makes-one-wonder