The books are a combination of origin stories (similar to the earlier Secret Origins series produced by DC), profile pages (like DC's Who's Who series from the 1980s), and short stories which sometimes serve as prologues to upcoming DC Comics storylines; early issues also featured timelines of significant events in the characters' histories. Some of these one-shots are released to coincide with a new series (such as the first JSA issue), or with a special event (such as the Infinite Crisis issue). Originally the books featured sequential numbering, but from 2003-2006 this was dropped in favor of putting the year of publication in the title (so for example, Aquaman Secret Files and Origins 2003 is the equivalent of Aquaman Secret Files and Origins #2); sequential numbering returned with the