In most software, the RAW files are not touched! Search on your computer for the original files. Also, never make the result of your NX2 or other photography processing anything but a Tiff* file. . I would really be surprised if NX2 discarded the original Nikon RAW file. Processing into .jpg should only be for delivery where that tiny file 8 BIT file is specified, as on the internet, posting here, for example.
Always work in 16 BIT Adobe RGB or better, Profoto RGB, which guards all the great data your camera collected), so as to maintain options in the future for making even better prints as software and hardware improves! sRGB 8 BIT have only 3% of your data!
I don't have Nikon files handy to test for you. So copy a set of Nikon RAW files and practice with the copies.
Asher
* RAW and .psd are subsets of Tif and in some MF camera software, .TIFF is the name of the RAW file as distinguished from .tiff