Technically, there should be an actual chart under there, right? Unless it was skipped because he knew he was going to put a BRE there.
The only instruments that need to have stuff charted are guitar and bass, for animations. The other instruments are all animated differently (i.e. not by the 5-lane playable expert part of a track)
Having said that, for 21CSM there is stuff there for Pro, but not for 5-lane. 5-lane keys has a bunch of random impossible to play things under there that I assume were put there just for shits and giggles. Simply removing the BRE lanes (and respective text events) WILL make 5-lane keys completely unplayable.
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