Wow, that’s interesting. I’d never read any estimate like that.
My personal experience with taller lace-up boots suggests there isn’t actually all that much stretching, even over many years. Partly, I suspect it’s that boots that high also tend to be heavier work or outdoor boots, with heavier leather, often pretty firm “alpine tannage” product. On the making side, I’ve learned that at least ideally, clickers align quarter pieces against the grain of the hides so they resist stretching when laced together. That’s the opposite of for, say, cowboy boots, where you want to click the shafts to resist stretching when pulled on by the straps or holes, vertically.
For cheaper boots, I expect they just click to get the most out of their hides, though. And I wonder whether stretching out isn’t more of an issue with softer-leather boots, like Thorogood’s moc toes, which I believe usually tumbled leather.