Recently i came across a situation in my local GW store where i had my Chaos Daemons and a Bloodcrusher of mine got shot with a Railgun. Naturally i pointed out the Eternal Warrior special rule and explained the Bloodcrushers did not suffer instant death. However the staff member cut in and said the Daemon special rule in the BRB didn't include Eternal Warrior anymore and takes priority being the more recent release. However this makes no sense, the FAQ makes no mention of this and if the entire Daemon special rule as outlined in the Chaos Daemon codex was replaced it would also take their Daemonic Assault and Daemonic rivalry away with it (and that's insane).
In the end the staff member forced me to remove the model and play by those rules, so obviously Fateweaver suffered instant death next turn and i lost badly. I'm sure this isn't right but when i argued i was basically accused of trying to cheat and would like some assurance I'm not mistaken as i was so outspoken on the subject it seemed crazy