I’m not sure if you are asking about two different things or the same thing…
I’m not entirely sure of the mechanics of it (why k2tbl), but I know it works. I just used it for the top of my Crazy Socks which I’ll be posting a finished picture of in in a few minutes. 
Now as to the first question…I can use stitches that have not been cast off for what? The i-cord bind off? Yes, that is the best way to do that, but I “think” you can p/u stitches and then do it, too. It’s been awhile since I made this sweater so I’m not entirely sure at what point I have bound off stitches and live stitches anymore.