Re: Attn: Logan Darklighter...or other Golddigger fans.
As noted, there are Perfect Memory books for the original Black and White comics that would probably include most of the info you're looking for. Since the start of the colour series he's been too busy with his other projects like the comic Legacy to do one. The Perfect Memories might be included in the Gold Bricks, I honestly don't know since I have the originals and never bought the Gold Bricks.
In the GD setting there WERE superheros until the late 1980's/ early 1990's, even Cheetah herself was a teen superhero and the sidekick of the Pink Avenger during those glory days. However, during the 1990's almost all the superheros (with a few exceptions, like the Pink Avenger) "retired" and dropped off the radar screen.
What had actually happened, however, was that they had decided as a collective that the public battles were doing more harm than good, and the "superhero" thing just wasn't working. So, with the American government's help they formed Zero Agency, an organization which doesn't exist (of course), and which is staffed by former superheros who are waging a covert war against crime and supercriminals as opposed to a more flashy public one. Basically, they're the superhero version of the Men In Black led by the former Superman of this world.
If anything, the world has actually been shrinking. Originally the GD setting was this huge and miraculous place, and it generally still is, but slowly he's been spending more time going back and revisiting than adding new stuff to the setting. He's also committing the "error" of constantly starting to tie things together and explaining too much in his geek drive to explain everything in his setting logically. As a result, the setting has actually been losing scale over time because in the end it's all the result of....Well, if you want to know that one, PM me. I won't spoil it for people.
Actually, I just started a GD-ish campaign last week, with the PCs being a group of adventurers working for the Archeological Royal Conservatory of Canada (ARCC) helping them deal with the pieces of ancient civilizations scattered across the world. Should be loads of fun.
If you have any more questions, feel free to ask. I know this setting pretty well.