"Not reported" for box C means that the sale was not reported on a 1099-B. But you do have a 1099-B, so you would not select box C. You have to select either Box B short-term noncovered or Box E long-term noncovered, depending on how long you owned the stock before you sold it. If you owned it for one year or less it's short-term. If you owned it for more than one year it's long-term. If you received the stock as a gift, you include the length of time that it was owned by the person who gave it to you. If you inherited the stock, it's considered long-term no matter how long you or the decedent actually owned it.
