Crusader Kings, Deus Vult and Patches

From Crusaderkings

Crusader Kings was originally released in PAL on August 27, 2004.

The expansion pack to it "Deus Vult" ("In the Name of") was released on July 31, 2007. The most recent patched version is CK: DV 2.1 Beta.

As DV builds upon and improves CK, including fixing bugs, it is strongly recommended that players play DV first. For instance, one bug you'll see in an unpatched CK is that numerous Counts and Dukes may pledge vassalship to the King of England- however, in DV declarations of vassalship are now more strongly tied to the titles one holds. (ie, King of England, King of Sicily)

It is also advised not to play old saved game files in updates of the game.

Also, note that most players play the latest edition of Deus Vult with the DVIP mod applied to it that improves the game. That's currently the most popular playable version of the game. (although other mods exist)