After reading 'A Thousand Sons' for at least the fourth consecutive time, skimming through Lexicanum and the Wikia pages, as well as rereading 'Prospero Burns' for the second time, I can't figure out why the Thousand Sons fought under Horus after the Fall of Prospero, and then continued to fight, on occasion, for Abaddon in the millennia after.
My point is, how the hell did they not know that Horus had tricked Russ into wiping them out, rather than bringing them peacefully back to Terra. Magnus was, after the Emperor, the greatest Pysker in the Galaxy. His sons, Ahriman and the like, sifted through the future (I know they were blind prior to the Fall, but in the immediate aftermath?) with their powers.
It is stated in the Wikia (I know its not entirely accurate 100% of the time, but I'm going to go with it), that Ahriman cast the Rubric immediately after fleeing Prospero and landing on the Planet of the Sorcerers. The Rubric swelled his and his already powerful fellow Legionaries into even grander Psyker's, but reducing the weaker Marines to automaton husks. Yet, the Thousand Sons still fought on Terra with Horus.
I just find it hard to believe, that the Thousand Sons (and Magnus if he gives a shit) didn't ultimately find out that the nature of their fall and casting as traitors was due to Horus' manipulations. And if they do in fact know that Horus was the one who manipulated him, why still fight the Imperium? The Thousand Sons were described as the most loyal of the Legions, I would think that their bitterness would be directed at their 'fellow' traitors.
Opinions and discussion would be great. If there is indeed fluff or canon showing that they do know of this,then could someone point me in the right direction plz.