When you have more than 90% mature cards, then the “Card Counts” chart is not informative.
I would like to divide the mature cards into two parts: Mature (> 21 days) and Old (> 1 year).
As in this screenshot:
Oh, my bad. I thought you were referring to the old stats where the young/mature distinction was much more prevalent.
Whatever categories and thresholds you use, it’s always arbitrary. For that reason, I find the Review Intervals diagram much more informative for review cards.
This parameter is necessary to track the achievement of the training goal.
Goal: Recall all cards after 1 year.
21 days indicator is a very short time for this goal.