Morning.

Very quickly....

So we know at the time of the razing of Prospero, the Thousand Sons were anything but Traitors. Their Primarch was certainly going a bit rogue, but entirely out of loyalty and ignorance of his actions.

In fact, I don't think it's yet been covered exactly when they threw their lot in with Chaos wholesale.

Therefore, there could well be covens of loyalist Thousand Sons during the Heresy, just as every Traitor Legion had them.

My question is simple - do we know if Ahirman's Rubric was Legion wide, or only those with him on the Planet of the Sorcerors at the time of the casting?