Well - at the risk of ticking off Ed I believe he is mistaken as well
There is no factory part number that I know of for a non adjustable 19mm rear sway bar. The 18mm was the largest non adjustable bar that Porsche offered for the 944 series. I've noticed that weather it is just from layers of paint or Porsche being generous that some sways measure larger. If you track down a part number I would gladly retract my assertions and retreat in shame