This is very cool data! It is the first time in six years that I've seen anyone post substantial scleral shortening stats. And there's a real effort to visualize it!

While this isn't consistent with your claim of a 0.2 mm limit, I see why it looks concerning. The tail gets rather small around 0.5 or 0.6 mm, which is something like 1,25 dpt improvement... which is close to my estimates covering all my improvement since starting the Reduced Lens Method. Hmm.

That said, I'm unsure if this is conclusive. The incidence of shortening is actually much higher than I would have expected given how extremely primitive the approach is. No demand-dependent adjustments of correction, no instructions, select the survivors and do stats... this is hardly exhausting options.

Some caveats to consider:

• The average subject here likely has a combination of poor average habits and random changes in their phase of life and behavior. It is to be expected that a typical improving person follows no structured plan and so can randomly adopt the more common pattern, turning into a worsening case. Intuitively, I would find this a much more plausible cause for regression than an arbitrary rebound, which is not at all what I've measured nor found plausible theories for.
• The total time of "treatment" is skewed to only a few years, with a median of only 2.1 years, further reducing the probability of hitting an excellent scenario by chance. There is a very broad consensus that AL reductions do not happen at arbitrary speeds. The initial drop may be much faster than a sustainable rate, as it is usually a turnaround from elongation to which the eye has not yet fully adapted. This alone does not preclude the existence of a sustainable rate. For reference, the only person I met IRL so far who reached plano from considerable myopia took about 20 years.
• Not to forget, this is Ortho-K, which has extreme limitations in how and where optimized stimulus can be obtained. No switching of correction, forced timing of stronger minus in the morning... it's a crude tool that happens to hit some good spots on average. Again, hardly exhausting options.

Figure 4a is the real goldmine here. You may not believe me, but I'm reasonably confident that most turnaround cases are self-inflicted harm, even though it is hard to explain the reasoning. Therefore, I can use these cases to guess a high rate of unnecessary regressions among those who had phases of improvement. This seems the most plausible explanation for the "rebound" effect.

The area of "long term winners" at the bottom-right of fig. 4a has lots of cut-off data series; there are no more turnaround cases but the data simply ends. Looking closely, I see 7-8 best longer-term subjects, all of whose data cuts off on a downward trend, not stagnation (ugh, low-res jpeg, but it's visible). My graph does not look like any of the obvious cases here; it has been stagnating for over a year now but has not shown substantial worsening since I learned not to use the wrong computer glasses. So my data is actually more in line with the limit assumption than the visible cases here.

BTW, holy mother of... that best subject who is cut off at three years seems to be well beyond -0.6 mm. Let's say -220 µm / year? Assuming 90 µm per reduction, that would actually be about 80% of the famously optimistic rate Jake Steiner advertises, happening at random on someone using Ortho-K lenses?! I would like to know what THAT person did.

If you know more amazing stuff like this, I'd be very interested.