Those refer to different Poser versions, which required slightly different material settings. PP (Poser Pro Pack, a sort of 4.5 version rather than the current Poser Pro) is the best one to use if it's there: otherwise you'll have to see which of P4 and P5 or later works better - since the labels were applied by humans their usage isn't absolutely consistent. Also, there is a script being developed (and available as a beta) that will read more information from the files for later versions of Poser so it may be worth trying that and perhaps keeping the P5 or alter files.