I dug out my copy, and this would be the full correct title. I'm currently going through it, to see what there is to offer. The edition I have is from 2002, and I'm aware that there's a slightly updated version that Twomorrows had released the following year. I'm not sure of all the exact differences between them, though one update may have been to cover Jameson Brewer's death in '03. Another change seems to mention Sandy Frank's plans for the redubbed/revamped "New Adventures of G-Force" series that ultimately fell through, and mentions the pilot having been completed.
Page 13 briefly references the two failed Gatchaman reboots of the '90s:
Gatchaman '96: Described as "a more "kiddyfied" version with super-deformed characters. The team would have included two female members and their base was to have been a massive flying platform. But aside from some very preliminary artwork, nothing further was done on this version."
(So either one of the guys would have been replaced by a girl, or someone at Tatsunoko was still trying to make a G-6 member happen. In that case, I wonder if the girl would have been the Hawk then, too...)
Gatchaman '98: "A lot of early production drawings and series planning were completed for the tentatively-titled "New Gatchaman" series but nothing came to fruition. The plans were to mix up the original with newer elements that would appeal to the current audience." Among the bits Hofius describes...
- New Gatchaman/Gatch 98 would be set in 2021.
- Berg Katse, Gel Sadora, and Egobossler each commanded a different Galactor army.
- Red Impulse squad is entirely comprised of women (so presumably something else happened to Kentaro)
- Ken and Jun are both searching for missing siblings (Between the very first idea for a Gatchaman sequel with Joe's brother and then this, the "long-lost sibling" plot point seemed to be a favorite)
There's a brief note on the NTT ads, but no indication if they were meant to spark interest in a remake or not.
Since the book's meant to be focused on the BOTP adaptation, the Gatchaman series and its sequels are kind of a footnote and it just barely gets into G-Force: GoS.