I had a stallion once whose foals all matured early and they didn't grow much in height after their 2 year old year, most were done growing as 3 year olds. Reading about your growth formula I can add that I have personal experience with 4 horses who were between the ages of 6 and 11 all permanent registered at well under 34" who after I got them grew from 2 to almost 6 inches more within a year.
There were 3 mares and one stallion, the stallion grew over 3 inches in less than 4 months! he was under 32". None of them were fat, it wasn't fat that measured taller. That's why I said the mature height has a lot to do with care and nutrition, I've seen how older ones will continue to grow..or in my case start growing again. I think even if stunted or starved in prior years, they will reach what should have been their genetic height with proper care.