Board Thread:Warhammer 40k General Discussion/@comment-173.238.152.115-20140122073927/@comment-6078851-20150410145237

well emps may have deleted the records regarding the 2 lost primarchs, but after his interrment in the throne whoever is the head of the inquisition has the authority to delete any records if they think it would benefit the imperium somehow.

and i'm pretty sure that the heresy is almost unknown of by the majority of the present imperium: astartes know and most of the inquisition probably know, they would have to really, but besides very few (proportionally speaking) high-ranking officials and military leaders the heresy is not known as the horus heresy. the vast majority of humans either know there was a civil war, or don't know there was a civil war at all - part of the reason that it's kept quiet is specifically because the chief antagonist was the favoured son of humanity's 'god', and faith in emps would suffer a serious blow if people knew that he made such a colossul f**k-up (which we all know is only one of many 'oopsie's' by emps :P). also the fact that fully half of the astartes were part of it, and public faith in them would be shattered if they knew that not only can astartes turn traitor but also their primarchs.

although i'll admit that i came across this info a few years ago and i havn't come across it since, so i don't know if it's been de-lored or not :)