Which he did, according to the legal definition of informed plea agreement.
Edit: to expand on this, the Court in Ruiz addresses the issue of whether the government’s failure to turn over some types of Brady material (impeachment evidence) rendered a plea involuntary and unknowing or uninformed.
Basically, unless Flynn can show his last Attorney was ineffective, or get the law changed

, he loses. I suspect he doesn’t want to allege ineffective assistance because that tends to inherently waive attorney client privilege and if his attorney comes out and says “we had candid discussions and in the course of those discussions he admitted he lied” then his chance at a pardon might go away.