Well there's more to it than that now, since the history of the DCU and Milestone have been stitched together so that now they think they've always lived on the same Earth. Even though "Worlds Collide" did still happen, I doubt they remember it since that storyline dealt with them on alternate Earths, something they shouldn't remember.
It was refered to in JLA. After "Final Crisis", Dakota merged with Earth-0. Only Superman, Icon and Dharma know the truth. Steel, Static, Superboy and the rest don't recall the exact details.