praise the Lord! You're the only person so far on this website to reach that level of 3000 fully learned. May God be praised! And thank you for setting an example for the rest of us.
excellent analysis! My impression (can't prove this) but my impression is that there is not a "dead zone"; but rather that the progress % increases at very small increments, once it's proportional to such intervals as 8 months. (The proportion of how early you are reviewing the verse to the actual interval). If someone reviews after only one week when the interval is 8 months, then the proportional % increase is very small, perhaps from 98.2 to 98.4%, but it's rounded off for our visual benefit, and so we don't see it until the whole digit increases.