Matching surface blues

The SS below show a 2 rail sweep being created from two profile curves created by duplicating the edges of the corner surfaces at either end of the rails. What I don’t understand is why when using the exact edge of a surface to sweep from it still fails to match up as per the Z lines. I then used match surface to match the ends of the sweep to the corner surfaces and yet there is still some imperfection and apparent gaps at the seams. The control points at each edge that was duplicated were absolutely in line - I used the scale to zero technique I learned from Kyle. In short I’ve done all I know to do at this point and I’m still coming up short. Is there some explanation to this?

Sweep results seam

After surface matching sweep edge to corner surface

Other end

after surface match.

Just an aside, but the “save” key combo - cmd+s stopped working again after about 30 minutes

Thanks (1.3 MB)