Merging Two Surfaces - Rebuilding Trimmed Part

I’m working on a dragon wings design, and originally I only wanted to create a double version where each side was a mirror image, so I trimmed off the end where I wanted the middle to be. I then, much later, decided that I also wanted to create a single wing version, but didn’t save any old enough versions and couldn’t figure out how to get back to a version where I still had the full shape (if there is a way to do this, let me know, nothing I’ve found has worked yet).
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Here I what I’m working with, with the part I’m trying to rebuild in red.
The current method I’m trying involved taking the original curves with DupEdge and making a new end with CSec and NetworkSrf with a curve from the original as the end point and then trying to rejoin at that curve. It’s hard to explain so here are some more images.
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I then tried to trim the old surface at the same curve, or even the DupEdge of the new curve, but it didn’t work. Here’s what that looked like anyway.
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I also played around with extending the surfaces to overlap but then I couldn’t figure out how to merge them.
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Here is a version of the file with the relevant parts isolated.
dragon wings single rebuilding.3dm (1.6 MB)
Any help would be much appreciated.

Hi Ace - Untrim should help here.

-Pascal

I had no idea that was a thing but wow that would’ve saved me so much time. Thank you!!