You would be wrong. The Neronian Legionnaires are suppose to be Necrorganic, that is why they have Necrorganic Resistance.
Not true. Neronians are necrobiotic. They have no leader model, and are, therefore, a Leaderless Squad.
The Legions of Algeroth:
Centurion Preceptor
Individual trooper, limit one per necrorganic squad, necrobiotic
(p. 452)
But Algeroth has no necrorganic squads!!
So?
I believe that they are included in the Algeroth list to provide for a Zombie Master in the event of the following:
In the event enemy model(s) are turned into necrorganics (Ragathol's Blade of Lost Souls), they'll need to be led. The Preceptor can perform this duty.
The army list contains necrorganics from the Hordes.
Further, it is my belief that the llimitation of "1 per necrorganic squad" is where the error exists, not that there are no Algeroth necrorganics. Simply change it to read "1 squad" and all should be good. In this way, they may be purchased in anticipation of having zombies to command, or may command necrorganics that are purchased from the Horde list.
By no means is my solution official. While I am on the FAQ Team, I am speaking for myself, on this one.