Reading over the online comics and few of my own collection I realized just how bad a kludge the writers had made of Krypton's history. For example in
Superman #141 (1960) were are told that Krypton has no space program in the time Kal-El parents are married and yet in an earlier story Jimmy Olsen had used a magical stick to send Superman back in time so Kal-El can meet his parents. But Olsen messed up and had it so Kal-EL would mate his parents. Kal-El has to save his parents who charged with some crime are exiled from Krypton in a space ship.
This causes all kinds of logic problems with Jor-EL sending everything but the kitchen sink to test his rockets; if Krypton had a space program advanced enough tp exile people than what the blazes was Jor-El testing? Elements in the Superman #141 story also contradict the Super-teacher stories. Then you have
Sun of Superman which conflicts with Action #574 in that the later story had a second planet orbiting Krypton's sun.
The story of Krypton's Second Doom from this stand point is just insane - we are asked that a planet that had little if any space travel could in a minimal amount of time build an artifical sun and a duplicate of Krypton so perfect that it fools Superman.
Did anybody actually set donw and straighen this mess out or was it largely ignored aside from the few times DC put out a digest with the older stories that made fans go 'Huh?'