The Independent Comics Group, an imprint of Eclipse Comics, specialised in produced indices of various DC titles and events, capturing a level of detail that puts to shame an enthusiastic annotations amateur like myself.
The two issue MILLENNIUM ILLUSTRATED INDEX was useful as I was going through the series, allowing me to capture one or two characters that I’d missed in some of the crowd scenes, and the synopses of the issues, both main and crossover, helped solidify my own thoughts in a few instances.
As an example of the amount of detail, here are the pages dealing with issue #1 of the main series:
Impressive, huh?
Crisis on Earth-Prime 