No priority seating is different from no seating. People's plans do change, and they usually aren't considerate enough to call dining. So...first, you can keep calling. Secondly (this is my daughter's version of the plan). You show up early in the day and ask for seating. Your sweet little one bats her eyes at the lady at the podium. Usually, they will tell you there's like a 45 minute wait, and then get you in about 15 minutes later!
My daughter is totally convinced that if she smiles and is polite, she will get whatever she wants!!! And it usually works.