No Sith tag for Asajj Ventress?

In one of the books on Maul, Plagueis was aware that Sidious had taken on an apprentice. He let him keep Maul for a while (before eventually ordering his execution). But while he let Sidious teach Maul the ways of the force, he specifically asked him not to teach him the ways of the Sith. They were separate things.

Also, on Sith Trooper again and why he could be a non-force sensitive Sith in his day. Sith were a nation, ruled by Sith Lords. There were Sith citizens who were nothing more than farmers.