I have used a row of crocheted chain stitch to stabilize the neck in a couple of sweaters, and it has worked very well. As someone said, the chain stitch is added where the body and neck stitches meet.
I've used elastic thread to pull in the bottom edges of many sweaters--somehow my ribbing often relaxes and flares out after a while. I even did this on my Hadley. I thread two or three rows of matching elastic thread through the back of the ribbing. It doesn't show, and it vastly improves the look of the sweater.
However, I would rather discover how to knit ribbing that hugs the way it's supposed to. One suggestion I read, for ribbing that's at least 2 x 2, is to twist the first knit stitch in each pair. Has anyone tried this? Or used other means to snug-en ribbing? I'd love to know.