The piano layers in a Program use samples, and the synth layers can also use samples from the sample library. As far as I can tell, a Program file doesn't refer to any samples that it uses by name. It seems to refer to them only by some kind of hash (maybe generated using crc32, but I'll just call it an ID number).
A partial list of ID-to-name conversions is built into ns4decode. The output from ns4decode will show the names of those samples next to their ID numbers in the output files, but for other samples, it will only show the ID number. That's the bad news.
Here's the good news: you can add to ns4decode's built-in list of ID-to-name conversions. The command
ns4decode --helpwith names