From my lay knowledge, a lot of the cluster b disorders stem from developmental issues (abuse, neglect).
I'm wondering in a prison population how many people could reasonably be expected to maintain a healthy personality. Prison features the abuses and neglect that mirror a bad childhood. The idea and philosophy of a prison itself is of inherent badness, and prisoners are in a way going through a reparenting process, which itself is controversial in the world of therapy but in the setting of a prison I don't think would be considered particularly healthy.
So I guess I'm saying if a person already had a personality disorder which caused a propensity to do things that landed them in prison, the prison might not be rehabilitative. But furthermore if you had someone on the edge of the propensity for maladaptive coping, then put them in the physical/mental stress of a prison, could you really argue that there is such a thing as a normal/healthy outcome? I feel like there are some situations in which the expected outcome of even the most hardy, emotionally balanced individual would be that the person would become messed up. I guess some don't, or at least they have the propensity to contain the pains internally. I mean Martha Stewart came out the other side OK from what we can see on the outside, but she was made of very stocky stuff before she went in and she had family support along with legions of fans supporting her.
As an analogy the military won't take people who have severe mental distress, but people who were mentally healthy enough to join will leave sometimes in a very mentally distressed way. Prisons are different in that they take people with a propensity for maladaptive coping and then expose them to more negative situations.