Fulfilling your wish, pulling stories from the far future, to the past of World War II, from the joys of the circus to the depths of the oceans, it is the last of the run of the 1970s Secret Origins issues, with the sixth and seventh issues of that series from January-February and March-April 1974 with covers by Nick Cardy and edited by E. Nelson Bridwell, and the origins of the Legion of Super-Heroes, Blackhawk, Robin and Aquaman.
Legion of Super-Heroesthe original story had a final panel with the original Invisible Kid entreating readers to read more of the important stories presented in that 80 Page Giant, the Secret Origins reprint wanted readers to follow the current Legion's adventures in the Superboy magazine.
The Legion would quickly add many members after that, including one of their inspirations, Superboy, the story of which happened in Adventure Comics #247 (which was the Legion's first appearance, where the Legion founders traveled back in time to get Superboy, then put him through tests to join their team).
Letters from readers also covered the Kid Eternity and Vigilante origins from issue #4, noting that Vigilante later had a page long origin in Action Comics #52.
Batman's time as Robin.
Aquaman got a little more detail as well, as his origin had been updated as well, with Adventure Comics #260 explaining how Aquaman had been born of a lighthouse keeper and a lady from Atlantis (more details from the origin reprinted in the More Secret Origins' 80 Page Giant, but...
....more improved Secret Origins would follow!