And then there was the Boy of Steel, the second superhero to appear on Earth-Prime after Ultraa's brief career there. Raised by Jerry and Naomi Kent after being found in a rocket ship, just as had his counterparts on parallel planets, the young Kryptonian lad discovered in his mid-teen years that he too had superpowers beyond those of mortal men. And it was during the Crisis on Infinite Earths when the Superman of Earth-One accidentally arrived on Superboy's world and helped the young lad in fending off an alien invasion. And then, as the Crisis crowds consumed Earth-Prime's universe shortly after Superman's departure, Superboy followed his older doppleganger back through the void.
Then, as the Crisis culminated, in order to defeat Anti-Monitor from consuming the remnants of the positive matter universe remaining the survivors of three Earths combined forces to ward off this threat. No longer in the new Earth-Zero's universe it was left for these individuals to craft from the memories of Earth-Two's Superman and Lois Lane a replica of their Metropolis in a pocket dimension.
And the Time Trapper of the new post-Crisis reality used his powers to create a pocket universe with a replica of Earth-One and its Smallville which mirrored that of Kal-L's Earth-Two Metropolis in a "paradise" dimension. Both of these had Superboys, not the originals but replicas of the pair, alongside Luthors that aided them rather than battling them as their counterparts had. Both realities ceased to exist and the Boys of Steel from Earth-Prime and New-Earth would be casualties to these Crisis.