Without having read the book, I'd go with A followed by D. The distinction among sorcery, witchcraft, and psychic powers is one of worldview, so I wouldn't be surprised if McNeil felt like it was anachronistic for Nikaea to use a term like "sorcery" - and of course the Legions couldn't use "witchcraft" by definition.
In a post-Heresy world, though, it makes sense to distinguish between sorcerous and non-sorcerous psychic powers, so I wouldn't be at all surprised if Guilliman wrote with that distinction in mind.
As for "slave" psykers ... Mel's right that slave psykers are a stupid idea, but where are you getting that in the first place, Fellend? The codex certainly doesn't say anything about slaves. All it says is that the Black Templars profess zero tolerance of mutants, including psykers, and thus do not fight alongside them - but that the chapter's various keeps and fleets stay in touch with each other somehow and navigate the Warp somehow, so presumably they must use astropaths and Navigators just like everybody else. The codex goes on to speculate that perhaps the Black Templars use only astropaths and Navigators that view their powers as a curse, and repent of their abilities. That wouldn't be so weird; plenty of Imperial psykers view their powers as a curse.