Best way to have two splines share a portion of contour? / Copy/paste portion of spline?

I’m in my second jam of this type. I have a base hair shape, and a highlight shape around it. I’ve decided to have the base hair contour the face rather than place a face shape on top. so after editing in the contour to the base hair shape around the face, I now also need my highlight shape to match, which has one or two extensions into the face area. How on earth am I suppose to get an identical portion of path, if I can’t copy and paste a portion of spline?

Count the number of vertices, and add the same number in the highlight shape, and then link each one (hoping I know the proper way to have that happen in the right direction)?

Memorizing these sorts of dead ends, making sure I never edit two shapes that share vertice positions, until I’m absolutely totally, and completely finished with every vertice they might ever share?

Copy the shape that has the vertice set I want, erase the unneeded portion, and then franken-stitch the two with by linking the vertices?

I’m sorry but all of these options are thoroughly hilarious for what should be a simple data copy and insertion.

Am I missing something?

I can’t even manage to stitch them together, I guess this is another niche skill. It seems the last node to be clicked before linking is the target value location, at least about 60% of the time. Highlighting all nodes and handles from two nodes causes all points to converge on the origin or something. And then, suddenly, without changing a thing I’m doing, by linking one corresponding control point from either vertice one at a time I can almost (almost!) link one node in place; but the last handle chooses the opposite position I want no matter which corresponding handle is clicked last. … this must be some very niche logic.