Except it's not as simple as you think because the number needed for individuals varies. Yes, there is an average, but it's only an average. People have different thickness of hair, head size, natural positions of hairlines, etc. You're also acting like it's a hard fact that it produces X amount and you forget that it's already been stated the process can be repeated. So how much a person is like to grow from one session likely depends on how good of shape their stem cells are in (age-dependent usually), existing medical or genetic conditions that might affect their response, how faithfully they follow the at-home regimen, etc. One person after just a couple months might have a considerably higher amount of growth than another, but it's not like the wounding can't be done again on the other person, nor that troubleshooting their lesser response is impossible. But again, none of this matters because studies have already shown it is capable of sufficient coverage without meeting a particular number outright.