All good points Gorillagirl. As you say these hairs could be something else (not true vellus)? We often call these hairs by several names: accelerating vellus hairs, intermediate hairs and (my favorite) “shooters.”
What’s happening is that in the field of real vellus hairs, a few are getting progressively larger due to a range of systemic causes. Indeed, it will take many growth cycles to finally see the “terminal hair” that the shooter will eventually become.
The term “terminal hair” means that the hair has reached the end, or the largest it will ever become … you know, like landing at the airports terminal. (I think the term is from Latin: “Terminus” … meaning the end point?)
Right now, we don’t really know what’s happening with this client. I totally enjoyed, however, your mathematics on this issue.
I hope the original poster does not feel insulted. She did ask for opinion and we are, actually, really trying to help.
The surgeon, with whom I work, says “no” to at least 50% of his potential cases. If a patient wants something that he feels is not warranted, or could harm the patient … he won’t do it. (Others will, and we often see “the horrible results of plastic surgery” all over the internet.)
A good practitioner will protect the patient … from herself!