>Targets of the OIG get notified with drafts weeks before the official version.
Not sure that is entirely correct.
If the IG, as part of his work, referred an item to an AG, then the AG might approach the target, or the AG might first get a Grand Jury indictment, which could in theory be kept sealed for awhile until they are ready to issue an arrest.
Usually, at that point, as a courtesy to the target, they may inform them of their impending arrest. Likely depends on the situation.