It's somewhat controversial because there are two camps:
(A) those who think that there is enough variability in hairs that two different hairs can show different interactions with the same blade, therefore HHT is not transferable between different hairs. I.e. me telling you how my choice of hair interacts with my razor is not going to tell you anything about how your choice of hair interacts with your razor (or my razor for that matter)
(B) Those who think that 'hair is hair' and me telling you how my choice of hair interacts with my razor means that you could reproduce the exact same behavior with your choice of hair, and therefore judge the same edge the way I judged it. (Or may be they mean a weaker transferability that if my hair interacts in a certain way with my razor, then if you make your hair interact the same way with my razor or another razor you will have very similar shaving experience.)
My body grows at least 5 different types of hair, and they interact differently with the same razor edge, so I fall in camp A and think my HHT result is completely meaningless to you because you do not have access to the same hair I am using, or if your hair happens to behave with the one I'm using it's a pure coincidence.
Of course, few years ago the biggest hurdle to people was to realize that HHT is not a yes/no test, but rather a nuanced test where one observes how a strand of hair interacts with the edge of a razor. So, attaching numbers to HHT is a progress in the sense that now people know to look for something meaningful, but as far as I am concerned there is no a priori transferability between people.