Fiesta Ware Markings I Collect Feista Ware. Some Are Marked W/Feista In The Material Before Firing And Some Stamped. What Is This.?

I collect Feista Ware. Some are marked w/Feista in the material before firing and some stamped. what is this.? - fiesta ware markings

Why do some courts have labeled w / stamp Feist and others in the materials before they fired, and some have no markings at all. I have a greater value than others. And the colors are there, a valuable than others. I have several pieces and I love her. Only interested in what I have. Is there somewhere I can a book about old and new Feist? Thank you for your time and cooperation. Marilyn