Mentions of "Necrolytes" throughout these sources may or may not refer to the clan.
This may be a euphemism for a more formally named clan, such as the Shadowmoon clan, who included necrolytes in its ranks. Perhaps it merely refers to the necrolyte class as a group, not unique to any clan. It is even possible that there was in fact an early clan in the Horde called the Necrolyte clan. This possibility is what is implied by Warcraft: Orcs & Humans, but later sources contradict this. If so, this clan may have later evolved into the Shadow Council, the Stormreaver clan, or a similar group loyal to Gul'dan. In Warcraft II: Tides of Darkness, the necrolytes are a subgroup within the "Warlock clans".
Similar confusion surrounds the rarely-mentioned Warlock clan(s).