By now it's known that the PIDs of all Pokemon from the Pokewalker come in the form D5FFFF??, possibly from an inability of the Pokewalker to handle 32-bit numbers. However, it seems the PIDs are also restricted by course. For instance, all the values of ?? for Pokemon from Winner's Road range from E8-FF. At least, all the ones I've caught. It probably ranges from E7-FF, in order to get the full range of natures. There are two applications to finding out the PID ranges for specific courses: