Howdy Guys and Girls :)
A new Errata is up for your Index Chaos - mostly point changes to daemons.
"Secondly, if you’re a Thousand Sons player, you may have noticed that the Dark Hereticus discipline in the new codex is larger than the one in the Index. Don’t worry – the discipline isn’t being replaced and you won’t need to get Codex: Chaos Space Marines to keep using it. Similarly, if you have Codex: Chaos Space Marines, you’re welcome to use the expanded Dark Hereticus powers with your Thousand Sons Psykers. If you’re a Daemons player, this change also applies to Be’lakor."