Same data, different results

Please see my screenshot attached.

I have a surface (1) which I need to join with multiple closed polylines.
These polylines come from two different sources: an offset node (2) and a scale node (3).
Grasshopper shows the same data coming out of these nodes, and same number of Polyline Curve, 100.
However, when I later use the Edge node, I get two different results, (4) and (5).
I need the one trimmed surface result (4), not the 100 surfaces.
Why do same data type and numbers produce different results?
What am I doing wrong?

thank you!

Can you attach your GH with internalized geometry ?

Right now I’m seeing potential tree issues due to the multiple wires in the same input, curves not lying on the same plane, tolerance problem… Hard to tell withotu the file.

Maybe you want to use Region Union before Boundary Surfaces also. The latter does not deal with overlapping curves.