A very common idea is that covert narcissism is where the manipulator hides who he really is. He initially pretends to be friendly to build relationships and then takes advantage of people later.
This, however, is a very common scenario for many people who are caught and abused by narcissists. In fact, many victims who consider that their abuser was a sociopath or a psychopath also tell similar stories.
The abusers, whether you label them narcissists, sociopaths or psychopaths, are not all stupid and they know that people won’t start a relationship with someone who is abusive from the word go. They know that they have to hide that aspect initially and they basically trick their victims into believing they are normal, caring, considerate human beings until they have some level of control over their victims and they then begin to take advantage. In this sense, their true nature was hidden. Hence the use of the label of covert narcissism.
But it is only hidden because the victim does not recognize the trickery being used against them. Oftentimes the friends and family will see what is going on but the victim is being emotionally manipulated in such a way that they are unable to think logically and rationally. They literally cannot recognize the danger. In this way the manipulation is covert or hidden, but it’s only hidden because the victim does not understand mind control or narcissism.
This occurrence is so common that it does not seem to me to be a useful description of covert narcissism.