Black Legion and Crimson Slaughter are supplements so require the core code for all the rules. They don't contain different units but have some extra rules for FoC (e.g. Chosen are troops in a BL army) a different Warlord traits table, alternative artefacts, cities of death and planetstrike strategems and some thematic scenarios.
The Khorne Deamonkin book is a codex in it's own right so has all the rules in there for making an army including unit entries.
Me: To be honest im amazed there isn't a chaos god of not revising or at least chaos god of procrastination
MidnightSun: There will be, when enough people do it. Y'know when the Eldar were all engaging in their hedonism and Slaanesh ripped open the Eye of Terror with his creation? Slaanesh will have NOTHING on the God of Procrastination, and his vile minions will carve the galaxy asunder in a thousand year reign of blood.... Tomorrow