Had success with a created loop with 4 sections.
Join the base curves.
Rebuild.
Extrude.
There should be only one target surface, with only one connecting line between the loop ends,
or in the case of a non looped ribbon, no separating line.

In the attachment. At the top is the base curve, before joining and rebuind, consisting of two arcs, and two blends.

Below is the extruded surface.


Please consider this to be an amateur response.

Loup (French for Wolf)

Do the curve segments need to be tangent?