Label on Underside of Sheet switch doesn't change the developed pattern.

It flips the Image on the Label so that when it is placed on the "underside" of the cut part it matches the part.

The Labels on Inside switch in Pattern developments is, as you say the one that flips the developed part to be cut face up or face down.

What is needed is a "per material" switch to flip the developed parts, as we cut some insulation types face up and some face down, particularly causes problems with external insulation developments.