"All I ever wanted was the truth. Remember those words as you read the ones that follow. I never set out to topple my father's kingdom of lies from a sense of misplaced pride. I never wanted to bleed the species to its marrow, reaving half the galaxy clean of human life in this bitter crusade. I never desired any of this, though I know the reasons for which it must be done. But all I ever wanted was the truth."
— Opening Lines of the "Book of Lorgar", First Canticle of Chaos

Yes, but the Liber Chaotica didn't have "to summon a Bloodletter, perform 'x'. To gain the favour of the Dark Gods, you should do 'y', 'r', and 'z'." A proper Book of Lorgar would have to deal with summoning the daemons, how to bind them to your will, everything people associate with Satanic rituals. That sort of stuff was kept well clear of in the Liber, and for good reason. I don't think parents would take kindly to a company selling a book to their kid on how to summon naked daemon-women, or any of the other daemons for that matter.