The actual specification that Nikon follows doesn't say that the folder number should be incremented every time you shoot 999 images. Instead, it says "if you fill a folder with 999 images a new folder with a higher folder number will be created." If, for example, you always shoot 500 images, transfer them to your computer, then format the card, you should stay at folder number 100 (you might not be still at 100 if you moved a card from another camera that had a higher current folder number, which gets recognized by the new camera). In general, you don't want folder numbers incrementing if you can avoid it. On the Nikon consumer cameras, the camera will lock when it gets to folder 999 and image 999, and it's a pain in the butt to fix that (on the pro cameras it is easy: just specify folder 100 and restart shooting).