Why doesn't everyone with male pattern baldness progress to a Norwood 7?

[M31]

I work with a guy that's been a NW3 or 4 for years on end, unchanged. We probably all know someone like this.

Why does the loss just appear to stop? Maybe they're just losing at a very slow pace? I think the man is in his 50's.

 

[SayifDoit]

I don't know what to say, the guy might be on propecia.
On the other hand male pattern baldness is unpredictable.

 

[zzzzz]

difference in androgen receptor counts between different areas of the scalp, some of which are not at the threshold where miniaturization will occur, or a change in hormone levels with age