I do not have sufficient knowledge to comment on the specifics of your enquiry but the following may help:
As Grant says, JPEG files are saved as 8-bit, so 2 to the power of 8. This basically means each R, G and B channel has 256 colour tone gradations. Combined, that’s over 16 million theoretically available. When you save a JPEG file you lose a certain amount of the originally captured data. Save, say, three times, and three different sets of data are lost, so further degrading the original image.
Raw files, on the other hand, exceed 8 bits. A 16-bit Raw file will give you 2 to the power of 16, so 65,536, for each R, G and B channel. Every device used, however, camera or computer screen, will be limited to what gradations it can actually display. Once processed the RAW files may be saved as 8-bit TIFF files which are lossless, or may be compressed to 8-bit LZW TIFF files for archiving. The LZW TIFF files may be reopened without loss of image quality. Always process in 16-bit first and then save to 8-bit.
For general photography I shoot JPEG Fine(L) and Raw together, and use the Adobe RGB colour profile, rather than sRGB, which would only really be used for JPEGs on screen or for posting on the internet. The JPEGs offer a quick check of the image and are often OK with little processing for editorial purposes. Occasionally, however, detail needs to be brought out of the shadows and for this I would use RAW. An example would be if you were to take an under exposed photograph of the moon and naked eye planets shortly after sunset, and you wanted to bring out some background details (e.g. trees), you are likely to find banding in a clear sky when processing a JPEG. With Raw you have more leeway allowing you to push the processing a little further. Processing, however, should always be kept to a minimum by trying to get everything as correct as possible in camera.
Nikon, incidentally, does its own RAW processing software which is freely downloadable from their website. If it is compatible with your camera you may want to experiment with that. You can convert to TIFF.
Another point which may be of interest is the exposure triangle: aperture, shutter speed and ISO. While it is true to say the three work together, it is only the aperture and shutter speed which lets in the amount of light whereas the ISO is the sensor sensitivity. I do not know which ISO you were using to photograph the moon. It is usually best to use the lowest you can, but some camera sensors have a S/N gain at a level higher than the base. For example, if I use my camera to shoot at 400 and need that little extra, I will go to 640 instead of 500 because that is where the S/N gain is. The S/N gain on your camera may be different. Beyond 640 the noise level again increases which may require more image processing.
Do have a look at your images on screen using the sRGB and Adobe RGB colour profile to see if that makes a difference to what you are trying to achieve.
Finally, a gentle reminder to always experiment with your less important images.