If it mentions Supra III, then the paper you have is more than 10 years old. You are lucky to get any suitable result from it as the Supra family was not noted for good keeping. It turned yellow and lost speed. Endura has pretty much fixed that problem, but no true color paper can keep as well as a comparable B&W paper developed in a color process.
The B&W paper you have has only one emulsion, not 3 and it has fewer layers and different chemicals to form the dyes. So, it is easier to coat and easier to formulate such that it keeps better.
Good luck with it.