Many times one sees the statement that all of Bach's manualiter keyboard
music can be played on an instrument with GG-d3 compass.
However, the D-major prelude for beginners on the keyboard, BWV936, calls
for e3. There is apparently no m/s in JSB's hand. Does this point to a
forgery, or original composition in C major? The passage certainly suffers
from playing any of it down an octave.
In any case, I find it odd that a piece for beginners should go higher than
any other piece by the composer.