Amazing-Man Comics was published by Centaur Publications from 1938-1942. The primary character, Amazing-Man was created by Bill Everett who would later go on and create the Sub-Mariner. Centaur Publications went out of business in 1942. By the 1990s the entire Centaur catalogue entered into the public domain. The series ran for 21 issues. The series started with issue #5. I couldn’t tell you why, but it’s probably because it recycled the numbering from a previous title. This was not an uncommon practice among comic book companies during this period.
In 1992, Malibu Comics tried to revive the Centaur line of heroes. It didn’t go so well and the line eventually ended. Incidentally enough, Malibu Comics was later purchased by Marvel Comics.
Anyway, Amazing-Man was later picked up and used by Marvel comics, first in The Immortal Iron Fist: Orson Randall and the Green Mist of Death. He later went on to appear in issues of Secret Avengers, and The Defenders as the Prince of Orphans.
As far as Marvel continuity goes only the issues of Amazing-Man Comics and Stars and Stripes that feature Amazing-Man comics are considered part of continuity. The Malibu reboot is not considered part of this continuity despite Malibu’s catalogue now being owned by Marvel (at least for now). For the purposes of the Unofficial Index, we will only be cataloguing the Amazing-Man stories featured in these issues in Amazing-Man Comics.
As Centaur Publications have entered into the public domain you can legally download every issue of Amazing-Man Comics for free. They are available on he Digital Comic Museum.