So a bunch of these extant bodices have some weird zig-zag thing which is holding on the boning channels.
Closeups:
WTF is happening here? The only way I know how to make a zigzag is with a catch stitch. It’s not the most secure of stitching, but it would hold a channel in place. It would also make it easy to take it out I suppose, in case the bodice needed altering or washing.
The boning casings here also look pretty intense. It’s not just a strip of fabric or tape. They’ve got a metal eyelet in the tops of the casings, and the shape of the bone is really prominent. It’s like the bones came in these fancy casings. I don’t know what this is.
Anyway, I experimented with a catch stitch on my boning channel (which is made of cotton tape from Joann), and I think it looks cool! I don’t think this is how the extant bodices did it, since the zig zag isn’t the same shape. You can see the points of my ‘zags’ aren’t as long.
Pretty! But probably wrong.
Would be nice to get my hands on a real bodice to examine…
Avant Garbe 
I am guessing machine we hope to get from Grandma may offer a lot more variety of stiches as well as more feet. Also- will have some heavy duty stuff that she says works well on denim. If you can recommend a cheap machine she can find easily, could speed the exchange. (What do they carry in Costco ? )
It would, although this is definitely something to be hand sewn.
Is this a varient of a herringbone stitch?…
I believe so, yes.
This is a faggotting stitch. I’m willing to bet this is ‘feather boning’ as this is a VERY inexpensive way to do this. Note the pinked (rather than finished) seams. It could be these are made at home bodices, because this is not how a professional would do this. The only scenario I can imagine for lots of these being extant is if it was an inexpensive manufactured, mostly if not all, ready to wear item. Mostly meaning there were items mostly made up by manufacturers that then could be fitted to the wearer and finished. The first pinking shear came out in 1893, which is about the time that partial ready to wear also came out.