Earth-15, a "perfect" universe, was destroyed by Superboy Prime during Countdown to Final Crisis. Even after Flashpoint, that was still true for the current multiverse, as stated on Multiversity Guide by Morrison. Morrison used again Earth-15 on #10 and #11 from his run on The Green Lantern, even showing souls of characters who died during Countdown to Final Crisis. Volthoom, the First Lantern from Johns' run, was also from Earth-15, that was told on one issue from Green Lanterns.