I'm afraid that I can't remember the reference, but I remember reading somewhere that 40% of people who have one dx of a personality disorder have a dx of more than one personality disorder.

You can have 'traits' that are in line with a personality disorder diagnosis, but not have enough of the symptoms, or not have the symptoms of sufficient intensity to warrant additional diagnoses. Knowing that you have traits of other personality disorders can be useful to know with respect to treatment, however.