Kurt,

It varies with the maarket. In 1985 it was a PX in the U.K and France and a PZ in the U.S., There was no PX in the U.S. for '85. In the U.S. SLX bikes became PX's and while 531P remained PZ's. In Europe it appears 531 bikes remained PX's. By '89/'90 they were getting away from the codes and going by model names.

Jim