P means Pro series. The Pro series use full 1" stainless steel joints piloted for an insert in the shaft, and are signed by Joe. They generally use "better" materials (exotic woods vs. plastics, more figuring in the maple) than the JP series.
The 16 is just a model number. The higher the number the more expensive.
They just came out with a new series which have a -F at the end, like P16-F.
-Mike