After quite some time of playing around, I found a perfect way to do high-quality NormalMaps over and over and over without any more dark model issues!
I replaced the NormalMaps for each version. I left the last version intact in case anyone doesn't like the new (much better) normal map for some reason.
It looks better, and I recommend just getting this version.
Version 1.1
I made a mistake when zipping the files with the original. I had included an extra root folder instead of zipping the "textures" folder itself.
Issue was raised to me by a kind downloader, and fixed promptly. You may now use NMM with this without any issues!