Accumulate the missed notes graphs to show progress for all playthroughs
At the bottom of the screen is the "song map" showing the entire song by sections and which notes have not been played, have been played correctly and have been missed. Why not add a box below this that shows the accumulation of correct and incorrect notes over time. This helps isolate problem areas. This could be as simple as a 1 or 2 pixel line, that shows the red/green sections form the last playthrough. And let the new box accumulate, perhaps showing the last 5 or 10 playthroughs. This would help a user better understand which sections they are really struggling with.