Retention for these documents is five years. I, personally, keep everything, but that's because I deal with a manageable number of exemptions and everything is kept electronically. I have an active folder for each exempt person and add my annual review to it every year. When the exemption is revoked or the account is closed, I simply move the entire folder to an inactive folder.
Don't make me say, "I told you so!" Sincerely, your friendly Compliance Officer.