I would guess that the mindset of someone suicidal will make them feel like they are less than they really are, while a narcissist for example will give them self a higher score.
I was with my ex for 23 years until c. 48, so I was 25 when I got with her. I was completely faithful to her in that time.
Between 16 and 25 I had about 25-ish sexual partners, some one night stands, others for 12 to 18 months.
As a guy I guess I always under estimated myself maybe?
I'd have said I was a low score, but then how did I manage to score at all? Some of them were really hot young ladies.
I always remember going into a nightclub with one of the ones I saw for 12 months or more, I'd chased her for ages. A guy was ranting to his friends about his lack of a girlfriend, and as I went past with her he shouted - look like I mean him - what does he have that I don't? I turned around and said - her...
LoL oh how I'd like to go back to being young again. If I had some confidence I could have achieved something.