When Privateer Press released Warmachine Mk2, they updated the rules for the entire existing model range simultaneously through the use of faction decks. These decks differ from an earlier product in that the earlier mk2 decks that were released had errata cards for Mk1. You can differentiate these cards because they have "2010" on the front cover.
Product codes and models included in the decks are listed below.
The image above shows you how the box cover should look.
Links to Faction Deck Contents
Uses of the Faction Decks
Buying a faction deck upgrades an existing model collection from Warmachine MK1.
