info re: picking up stitches to finish arm hole edges and neck edge

[Christinechrstms1]

Hi everyone, I am almost finished knitting the Lillian Tank
http://deliciousstitches.blogspot.ca...-tank-top.html

I am wondering, at the part where I am to pick up the arm hole stitches and the neck stitches to finish the tank with ribbing, do I pick up each and every stitch or not all of them. If I pick up all of them I am thinking that the neck line may be flimsy or saggy but I am not sure. I thought I read somewhere that it isn't always necessary to pick up each and every stitch to finish the edges.