That whole event definitely falls under big-summer-crossover exemption. Like the time in 'Superman' how Zod captured every meta on Earth (including Catwoman or Batgirl), or those few early JSA stories which featured world-ending-type-situations, none of which get referenced anywhere else (even though, in a shared Universe, they should be).
It's just how comic book continuity works. I'm surprised it's still an issue these days.