If I remember correctly, either Superboy or Luthor Prime or possibly both were introduced a few years before Crisis on Infinite Earths. I believe it was in DC Comics Presents. Back then Prime Earth was supposed to be our Earth.
Actually, neither character made their appearance before the Crisis
(well, there actually was no Luthor Prime. Are you thinking of Alexander Luthor, Alex Luthor's father, the only hero on Earth-3? I can't find a record of his first appearance, unless it was in Crisis on Infinite Earths
Superboy Prime made his debut in DC Comics Presents #87
, which was dated November 1985. CoIE
began in April 1985.
Okay, thanks. I guess I misremembered some of that, but that's cool. I should go back and re-read the original Crisis again as it marked an end of my DC reading days for a good long time afterward.