I do believe in terminal length, but I don't think you can determine it by the diagnostic given in your poll, which is not seeing any length retention. I mean, for a great many black women, their hair stays at shoulder length or shoulder for years and years, maybe all their lives. Does that necessarily mean that their terminal length is just a few inches? Probably not, just means they're not doing what it takes to retain the length.
Hmm, how would one know? Maybe if you cut your hair down to a near baldie and gave it like a month to grow, no more, then dyed it. Let your hair grow without cutting it and wait until the last few strands of dyed hair fell out, assuming you managed to retain that initial 1/2" or so for its entire life time. You have to wait until the last of the dyed hair sheds because, just because you cut your hair, doesn't mean the hair's life span starts over. So some of those strands have already gone through a lot of their life. But some of those hairs have to be at the beginning of their cycle. So you don't cut those, and if you can keep them until they shed (you'll be able to recognize them because of the dyed ends), you can figure out how many inches and time it took for that hair's life to end.
Does that sound right to everyone?