Hi Kevin, I had a quick look at this if you didn't mind, and as Michael says that yellow curve can't be included in the building of that surface or else it won't be smooth, it hasn't got the same curvature as the other cross strings, unless you intend to project that curve onto the surface or extrude it in the x minus direction to trim with.

Anyhow, for what it's worth I've attached your wing tip showing a plane that I used to extend the curves, then swept the last cross string and used the resultant edge at the end for the last cross string for a network, as you can see the surface is quite smooth but the yellow curve you mentioned is nowhere near that surface.
Another thing I noticed is that the main curves you have there have a lot of control points, was this a result of it being a projected curve ?


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