The chronologies of Aquaman and the Atom are screwy. Most chronologies place Action Comics #480, 481, 482, 483, then Showcase 100 prior to JLA 155. Atom reversed Action and Showcase, while Aquaman moves Showcase until after JLA 155.

While trying to work that out, I found Secret Society of Super-Villains #12 having conflicting chronologies for Batman and Captain Comet. For Batman SSOSV 12 occurs prior to JLA 155. For Comet, SSOSV 12 occurs after JLA 157.

Green Lantern Action Comics #480 (February 1978): "Amazo's Big Breakthrough" Action Comics #481 (March 1978): "It's a Bird, It's a Plane, It's Supermobile" Action Comics #483 (May 1978): "Sleep No More" Challengers of the Unknown Vol. 1 #87 (June-July 1978): "Twelve Million Years to Twilight" Showcase #100 (May 1978): "There Shall Come a Gathering" Justice League of America #155 (June 1978): "Under the Moons of Earth"

Flash Action Comics #480 (February 1978): "Amazo's Big Breakthrough" Action Comics #481 (March 1978): "It's a Bird, It's a Plane, It's Supermobile" Action Comics #483 (May 1978): "Sleep No More" Showcase #100 (May 1978): "There Shall Come a Gathering" Justice League of America #155 (June 1978): "Under the Moons of Earth"

Justice League of America Action Comics #480 (February 1978): "Amazo's Big Breakthrough" Action Comics #481 (March 1978): "It's a Bird, It's a Plane, It's Supermobile" Action Comics #483 (May 1978): "Sleep No More" Showcase #100 (May 1978): "There Shall Come a Gathering" Justice League of America #155 (June 1978): "Under the Moons of Earth"

Atom Showcase #100 (May 1978): "There Shall Come a Gathering" Action Comics #480 (February 1978): "Amazo's Big Breakthrough" Justice League of America #155 (June 1978): "Under the Moons of Earth"

Aquaman Action Comics #480 (February 1978): "Amazo's Big Breakthrough" Justice League of America #155 (June 1978): "Under the Moons of Earth" Justice League of America #156 (July 1978): "The Fiend with Five Faces" Aquaman Vol. 1 #62 (June-July 1978): "And the Walls Came Tumbling Down" Aquaman Vol. 1 #63 (August-September 1978): "My Brother's Keeper" Showcase #100 (May 1978): "There Shall Come a Gathering"