Mobs that directly drop the plans seem to drop them on the first try, happened on my elemental shaman n destruction warlock but now I'm struggling with the other Warlock speccs and the Deathknight ones too..just tried to get the Blood one, nope not in the big chest at end of Withered army training...
Also apparently my druid n warrior still need exalted with factions to even get any hidden artifact at all..
Sure this patch made things easier, but still a pain it seems...