Who knew time-travel rules were so complicated?

I was thinking of DC's old rule, that you couldn't go back in time to a period where you already were, as seen in Brave and the Bold #192: Superboy is brought to the present, which launches Superman back to dinosaur times. I think it was the universe's defense mechanism, to keep you from running into your past self and causing a paradox. But there was another rule where time-travelling to when you already were turned you into a phantom...huh. From 1982, DC Comics Presents #51, "Rendezvous with Death" Written by Dan Mishkin, pencils by Alex Saviuk, inks by Frank McLaughlin. There's a nice cover with the Atom on Superman's grave, swearing vengeance, although it would be hilarious if his word balloon was really tiny...

The Atom had long had access to his friend Professor Hyatt's invention, the time pool: it opened a portal through time, but only one small enough for Hyatt to "fish" through with a magnet, or for the Tiny Titan to use. What I didn't realize, is that Atom had been using it without permission all this time! He catches an earful later, but there are bigger problems: Hyatt had pulled a piece of technology from the old west that shouldn't have been there. When Atom went to investigate, he became an immaterial phantom, which had never happened to him before on these trips. Worse, he thus can't help Superman fight a group of aliens, who proceed to vaporize the Man of Steel! Barely getting back to the present, Atom heads to the JLA satellite, where he finds Superman alive and well.

Examining the tech Hyatt found, Superman recognizes it from another time-travel case (and one that was mentioned in passing in the Krypton Chronicles) as belonging to his great-grandfather, Var-El! He had been a scientist, and had gone to earth to conduct experiments illegal on Krypton: that sounds ominous today, but every so often the planet seemed to turn on science a bit. Var-El had been believed to have been killed in a lab accident, but maybe not. With Professor Hyatt--who's thrilled to finally get to travel through time himself--Superman and Atom go back into the past; and the Atom doesn't ghost out this time.

In the past, after some scuffles with the natives and the aliens, Hyatt is saved from a bear by Var-El, who had been chilling on earth since being saved from that lab accident by the aliens. The aliens were big on execution but short on ideas: they wanted to advance their own science, but couldn't really come up with the breakthroughs to move forward. The aliens had been looking for Var-El, who now had super-powers; but also wasn't up to a life of adventure. Worse, Hyatt tells him the entire publicly known history of Superman, including Krypton's destruction; but Var-El might be more freaked out considering a future where he was dead. Still, Hyatt's able to talk him into helping his great-grandson.

In the energy trap Atom had seen him before, Superman tells him "history can't be changed--but I never try to second-guess it!" He had a plan to save himself, but still gets vaporized. The Atom attempts a suicide run to avenge Supes, possibly because he was his ride back to the present and he doesn't want to live in the 18th century. Still, Superman wasn't dead: he had saved himself with the Atom's shrinking trick, then saves the Atom from destroying the aliens' satellite like a human bullet. The aliens are stopped, although Var-El is killed in the battle...seemingly. After everyone returns to the future, he meets with Hyatt, who had told him how Superman traveled through time: Var-El wanted to come to a future where he wouldn't just be "a lost footnote in history!" Which made me doubt if he would appear again pre-Crisis, but he did! Maybe we'll see it someday.