Every completed round is recorded against a nickname. This is what those rounds add up to.
For the player
Score for each completed round, oldest first. What matters is the direction, not any single round.
Share of shots on target for each word class, weakest first. This is the one that says whether the metalanguage is actually sticking.
For you
How many rounds were attempted at each stage in Classic, and how many of those were failed. The wall, if there is one, shows up as a drop.
Rounds played per day. Gaps are as informative as the bars.
Csikszentmihalyi's point about flow is that engagement collapses at both ends — too easy is as fatal as too hard. When someone stops playing, the interesting question is which end they fell off.