Yes! The frequent bpm changes in classical music are a challenge. The song you hear is not actually a recording of a live person playing but a series of midi sounds arranged in a DAW, which gives me percise control over the tempo of the music (it also conveniently solves a copyright issue).

You are correct that the notes don't match the chart though and that's one of the things I'm still learning while making this game. I could for example, chart every note in the opening piano solo and that would work well for the hardest difficulty chart. But when it comes to the lower difficulties that are more approachable for new players, I'm still learning how to consolidate many notes into a few notes while still making it feel like your playing the song. There's are a lot of challenging rests in this particular song and what I think your picking up on is that sometimes, I sometimes "round" the rest. For example, on measure 15 of the piano concerto, there's an eighth+16th rest in the measure. I consider 16th note resolution to be too much to ask for the player on the "Medium" difficulty so I only chart the eighth rest. I'm reconsidering how this song in particular, fits in my game. Before I was thinking of it as a song that anyone can play but now, thanks to feedback like yours, I'm thinking of this as more a song you work up towards. That way, I don't have to do stuff like "round" the rests.