I've been making stock from chicken bones (and feet, when I can get them) forever, as I learned from my frugal mother, bt it never occurred to me to make it twice, or thrice, from the same bones. I usually just cook it longer to get all the goodness out. But perhaps I will do that next time. One thing I do NOT do is salt the stock (which is recommended in the first link above), either before, during, or after the cooking. I save that for the finished dish, whatever it might end up being. Salt isn't necessary for the stock making process.