True, many people with NPD are not aware they are narcissistic and would deny it if they were in fact diagnosed
I have met only a handful of people in my lifetime that I would say fit the diagnostic criteria for NPD. Either I have been very lucky or 1 in 6 is a huge overestimation.
Being treated badly in a relationship, at the end of a relationship or after it ends does not mean a person is a narcissist. Just like an episode of rage or envy does not mean someone is narcissistic. It is prolonged behavior, not episodic.
Some info below:
In the American Psychiatric Association’s Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5), [1] NPD is defined as comprising a pervasive pattern of grandiosity (in fantasy or behavior), a constant need for admiration, and a lack of empathy, beginning by early adulthood and present in a variety of contexts, as indicated by the presence of at least 5 of the following 9 criteria:
A grandiose sense of self-importance
A preoccupation with fantasies of unlimited success, power, brilliance, beauty, or ideal love
A belief that he or she is special and unique and can only be understood by, or should associate with, other special or high-status people or institutions
A need for excessive admiration
A sense of entitlement
Interpersonally exploitive behavior
A lack of empathy
Envy of others or a belief that others are envious of him or her
A demonstration of arrogant and haughty behaviors or attitudes