I'm covering these three as a group as they're similarly formatted. Each book takes a different heroes and covers books in which they place a feature (not guest or part of team) role up to the mid-1960s (except for Brave and the Bold appearances). Characters, key locations, etc are covered alphabetically. Every key character in a given story in their adventures (in Fleischer's opinion) is covered. Incongruities in the text are noted and chasracters' psychology is examined.
Book 1 is Batman, Book 2 is Wonder Woman, and Book 3 is Superman (the Great Superman Book). Superman was originally intended for a later volume, but the series got cancelled prematurely. Possibly the Superman came out (much later) to coincide with the Superman movie.
There is some overlap of entries in the Superman and Batman volumes due to team-ups. Even so, all three volumes are a great resource for people wanting information on the heroes' early years. Don't let the fact that these books came out in the 1970s put you off from trying to find all three volumes.