I just went back and re-read Liam Lawless' article, and it is striking how close it is to salt printing. The only real difference is a bit more gelatin ( around 4% ) and a mixture of sodium chloride and sodium citrate. The short self life and most everything else he describes about making the print is nearly the same. Some people add sodium citrate to salting solutions for salt prints, and some people add higher amounts of gelatin. So in the end, the most important difference would seem to be that the silver nitrate is mixed with the gelatin prior to coating, instead of coating in two steps.
Also, his article must be describing something different than what was sold, since it has a short shelf life like salt print paper. The commercial POP must be more of an emulsion.