The problem with the original post is that you are assuming that:
a) Admiral Nok knows the whole truth about the Family and Dassem's role in it
&

We have the example of Hawl to demonstrate that at least one of these assumptions are false. Either Nok didn't know she lived (so what else does he not know?) or he chose not to reveal it (so what else was he not telling?).
I think the main evidence that people cite from NoK is this (NoK spoilers, but many people don't have access to the book and I'm not giving anything away by revealing that Dassem didn't actually die at Y'Ghatan, since we know that by this point in the main series anyway).
That's interesting, you can't include a quote inside a spoiler.