Valence 592 is the 1st Edition of the Valence game, published as free HTML and a compiled PDF available for download. In addition, the game manual was available as a series of PDFs for each major chapter. The GM's Book primarily is concerned with the setting and timeline of the Valence universe - information that, it is assumed, the players will discover through the course of the game.
From the master timeline:
This is the "official" way things happened in the universe of Valence 592. As you get into the last part of the timeline - the "future continuity" section - events might get in the way of your own campaign. Remember: don't enslave yourself to this timeline! Run your game however you want. This is just the "official" way things turn out. If your game would run better with things happening at different times (or not at all), so be it.