HH setting makes a few of the remarks about the whole thing. The Red Thirst was there from the beginning, the black rage came later.
What sparked black rage is somewhat unknown still but it cemented down the lineage once Sanguinius died, thus why it's "death visions of sanguinius". The lore is a little all over the place and it's likely something that was done sometime during the siege of terra since everything written about what the visions are so far revolved around some conflict during that time and not before.
"The Black Rage first appeared after the Heresy.... Specifically after the Sanguinary Priests drank Sanguinius' blood."
That is not quite correct. It's not currently written to be directly tied to the consumption of blood. But proving either way is hard since all BA drink the blood to activate their geneseed. Prior to Signus and Terra, it was the thirst that Sangunius tried to hide, not some form of black rage. The written fluff so far shows that Signus released a form of it while during the siege it came full bore after Sanguinius' death. From my own perspective, it sounds like the curse was probably created during Signus but it was the Siege that allowed the fell powers to rubber stamp the malady across all the Blood Angels. Perhaps some sort of psychic wound which was then reopened and infected during the Siege. The damage so ingrained that every geneseed has the potential to reopen and control marines.
Primaris being affected by black rage is the interesting bit. We don't know as readers if their geneseed was taken before or after the Siege of Terra or even before/after Signus. It's possible it was after the Siege but there isn't really a clear start/end on when Cawl started his harvest. Being tied to the blood may also be an indicator of sorts in that it activated a dormant part of the geneseed. So initially parimaris weren't having issues until their geneseed was activated with actual blood lineage. Again, not really spelled out so pure speculation.
I haven't read "darkness in the blood" so I can't speak to what the most recently take is from the BL writters themselves.
Edited by Spagunk, 22 November 2020 - 09:30 PM.