US v. Hariston: Hairston was convicted in 2003 of a drug conspiracy charge. His sentence was based on a Criminal History Category IV, which was calculated including a prior North Carolina traffic offense that occurred during a time in which, Hairston claimed, he wasn't in North Carolina. He subsequently filed a 2255 that was denied. He also filed a motion in North Carolina court to have that conviction set aside. That motion was granted, in 2011. Shortly thereafter, Hairston filed a new 2255, seeking a resentencing based on a CHC III. The district court dismissed the motion as an unauthorized second or successive motion.
On appeal, the Fourth Circuit reversed. First, the court rejected the Government's argument that Hairston had waived his right to challenge the prior conviction via his plea agreement because, ironically, the Government had failed to raise that argument at the informal briefing stage. In other words, the Government waived its waiver argument (ha!). Next, the court concluded that Hairston's second 2255 was not "second or successive" because it was based on facts that weren't available to him when he filed his initial 2255.