Unless you have a hardmod, you very likely made that NAND.bin after you've downgraded. As I've said in my previous message, downgrading doesn't give you a clean 9.2 firmware, because some files don't actually downgrade (unsure why, maybe to prevent bad sig checking resulting in bricks?)
If you don't really care about that though, you could probably sell it at 9.2 for a higher price.... If that's the case, restoring NAND.bin to sysnand will work, and you can do that by putting NAND.bin on your SD root, going to gateway menu (no flashcart needed), and holding Up when pressing A on "Downgrade Console".