That's the problem, 4th edition book was not a proper Army Book, it was a WD compilaton book, and that's one of the motives that they claims to remove them during 6ed.
Tamurkhan was not a proper army book. It was intented as an Chaos Warrior Ally Faction and it was not intented to be played alone.
If we are strict with the words, the Chaos Dwarfs never got an Army Book