Here’s a website that describes overt and covert narcissism.

The covert narcissistic personality, like the over narcissist also lacks a conscience and will project his or her damaged inner self on to others by lying, manipulating, withholding or abandoning –using whatever tactic gets a reaction and hurts those closest to him or her. …

… Just like the overt, the covert narcissistic personality type is highly exploitative and believes he or she is entitled to take, but has very little interest in contributing unless there is an ulterior motive attached.

So the differences between them are basically superficial. If they both lack a conscience, their awareness, either of themselves or others, is pointless as it wouldn’t lead to the necessary empathy to treat people respectfully.