There are two parts of this ballet - first, Curves have normals, they are drawn like arrows. Where is the ‘first point’ does not really matter, what matters is all curves in one set should point one direction, normals, arrows.
And the second part - it matters how curves are added to the set. When GP is used (and it is shown in all mentioned videos) you can’t expect normal result if you draw two strokes and the third stroke in between of two previous ones. You’ll get a looped something - Bsurfaces follow order in which strokes are put.
Same goes to curve set - if you start from one curve spline, copy, move, then copy again and move in between two - this wont work.
It used to be you could draw one more GP line crossing previously drawn to tell what is the set sequence - this does not work now.
You need to P disassemble set and J join curves following the 1,2,3…n order. While your two sets had properly oriented normals inside the set, directions were different between the sets. Then, i am not sure what sequence curves would get if you join sets where you reorient normals in one set. Probably something will go wrong, so disassemble one set and try adding to another. I that was some ship’s belly i’d rather start fresh. There is no way to tell what is the order curves get added. No indication, all you’d see is tangled or fine mesh.
There is one more illness to the Bsurfaces right now - it unchecks your Global Undo in user preferences. As a result - done some Bsurfacing - no more Undo and any added after primitive has disabled settings. Use Bsurfaces - go check back Undo in UserPrefs, temporary, hopefully.
Rumors go there will be BS2 for the next Blender’s versions. I did mean Bsurfaces 2, ofc.