Annie,
I believe those using NA2 are not using any other platinum in the solution. The NA2 becomes part of the image along with the palladium. The more NA2 used to boost contrast the cooler the image becomes, somewhat like adding platinum. I use potassium oxalate dev. with dichromate for contrast control and use very small amounts of NA2 to kind of tweek the contrast. I thought I really came up with something new until I went to APIS this year and found out many people were doing the same thing.
Wm Blunt