If you set the calculator to supply more bioenergy than is used e.g.:
Then the value of vector Y.04 Coal oversupply (imports) includes that oversupply, where it perhaps should have ended up in the Y.01 Biomass oversupply (imports) vector.
The emissions sequestered by growing the biomass are also counted, even though the biomass is available for export. It is not clear whether or not this is the right thing to do, given that bioenergy imports are counted as zero emissions.