Whether or not the supervisors expect to be flattered does not affect the argument. We need to link the obviousness of the flattery to not usually causing promotions.

These are official guidelines, but we have no assurance that supervisors follow these guidelines. It is also a small assumption to say that this merit criteria does not include flattery (though we would hope not).

We cannot invoke this conditional in context of the stimulus. In the argument, the flattery is noticed—this would negate the sufficient condition of (C), i.e. flattery is not noticed, but negating a sufficient doesn’t allow us to infer anything.

We don’t know whether the flattery discussed in the stimulus is sincere or not. Even if we did, we still wouldn’t know what effect sincere admiration would have on causing or not causing a promotion.

This is the link that we needed and predicted. This allows us to join the premises (flattery is obvious) and the conclusion (flattery doesn’t usually cause promotions) in a way that allows the conclusion to be validly drawn.