Contrary to the right's desire, not every mistake is a conspiracy. I don't think he actually argued any of these before SCOTUS. He signed a brief. Who knows how those were collected to be handed over before his confirmation. He could have been assured they would be in the pile and then a secretary didn't put one pile on top of the other.The six briefs to the Supreme Court were not Holder's work alone. In every instance, he was one of a group of prominent lawyers or ex-judges who signed a friend-of-the-court brief.
I see he gets no credit for coming forward with the mistake.
It may not be a non-story but, it's pretty close. Would you believe a simple explanation? Or would you want to ?