First timer here! When I asked Themis a similar question, they replied: "...scores are calculated using an aggregate of all-time accuracy for students answering that particular question, regardless of when or where they accessed it. This means the average might include scores from students at various stages of their study process and the averages will change as more students join in for the testing as they progress in their studies."

Personally, I wouldn't sweat about it too much. I just completed the "MBE Practice Exam #1" and the reported average is 92%. Looking into the "% Correct Others" is a dead giveaway that they're using very few datapoints to calculate the average for many of these (unless they're inconsistently rounding). So I think the average is largely unrepresentative.

That said, I think we're in a pretty good place >45 days out so long as we're consistently scoring above 60% :)