The majority of the rulebooks for 1st edition have been combed through, the ones currently remaining are Space Hulk, it's expansions and the Vehicle manual. Once that's done the only thing from 1st Ed should be White Dwarf content that wasn't added to one of the many compendiums and whatever novels might have come out at that time. I've attempted to get everything EC and slaanesh related but there has been some generic chaos and lore for other legions/gods that has been left out for relevance, but perhaps that I should have added it, I'm unsure.
But once the remaining six books are done, that will be the entirety of the legions lore from the 1st ed rulebooks.
But once the remaining six books are done, that will be the entirety of the legions lore from the 1st ed rulebooks.