unfortunately, I don’t see any way of detecting what difficulties a song has charted beyond opening it in reaper and comparing the charts. even a midi parser would see that EMHX have charts, but do we really want to start comparing note by note to provide the final result = “this is an x-only song”? I at least don’t see the use in that.
You know what? It’s a matter of counting the number of Note events between notes 96 and 100 and comparing to the total count of the 3 lower ranges. If there’s a MIDI parser than can give you the notes count, it’s actually very easy to do that, come to think of it. If total count is bigger than, say, 10 (because some charter just place some notes on the chart to satisfy Magma) and it’s lower than the prevoius difficulty level (starting from Expert), the difficulty is authored.