Maybe change Page_Load into Pre_Render .... though I wouldn't if you can keep it all in Page_Load

there's loads of thing sit could be. Try setting it in ViewState and even holding it as a session var - but it can get tricky.

If you bind all of your data in a function then call that function again within the edit  and update  commands.

 public void List_Edit(Object sender, DataListCommandEventArgs e) 
  {
   list.EditItemIndex = (int)e.Item.ItemIndex;
   //BindPagedData();
   string itemID = list.DataKeys[list.EditItemIndex].ToString();
   double price;
   int qty;
   string itemName;
   string sItemDescn;
   int discount;
   string disctype;
   string img;
   bool inStock;

   // get details about item   
   Item item = new Item();
   item.GetDetails(itemID, out price, out qty, out itemName, out sItemDescn,
    out discount, out disctype, out img);
   //inStock = qty > 0 ? true : false;
   //Change this as I shall be adding up the items purchased, starting at zero.
   inStock = qty > -1 ? true : false;

   //Response.Write("itemID : " + itemID + "   price : " + price + "   itemName : " + itemName + "   itemDescn : " + sItemDescn + "   img : " + img);

   Session["currentSubItem_R"] = "..... " + sItemDescn + " is in <b>edit</b> mode.";
   ViewState["currentSubItem_L"] = Session["currentSubItem_L"];
   ViewState["currentSubItem_R"] = Session["currentSubItem_R"];
   currentPage = (int)ViewState["CurrentPage"];
   currentItem = (string)ViewState["CurrentItem"];
   currentSubItem_L = (string)ViewState["currentSubItem_L"];
   currentSubItem_R = (string)ViewState["currentSubItem_R"];
   BindPagedData(); ....................................................................this is my main function that binds all the data ... it is also called from page Load
  }

  private void Page_Load(object sender, System.EventArgs e)
  {
 if (!IsPostBack)
   {
    currentPage = 1;
    BindPagedData();      
   }
}

when you response.Write(Addrow) what does it print out ?
You just need to get the whole pages structure regards load order and postbacks and events in the correct order.

Binding in Pre_Render may do it - but if you get into that habit you end up loosing a bit of leaway when it comes to importing and nesting controls in a page.