I currently work with two D700 bodies and a new D800 body. To keep images easily separated, I renamed the files in my oldest D700 A01_XXXX; my other D700 has files named B01_XXXX. This morning I will set my new D800 up as C01XXXX. Of course, the four "Xs" are the file numbers your camera creates. As I approach 9999, I simply update the first three characters. I have shot about 37,000 images on my oldest D700 -- thus its latest file is named A04_7000. When it approaches A04_9999, I'll change the prefix again -- to A05. I doubt if the camera bodies or I, will outlive this system! My Nex camera body will produce files labeled D01_XXXX, and so on. Make sense?