Any tobacco of a certain type which cannot be placed in other groups of the type, or any nested tobacco, or any muddy or extremely dirty tobacco, or any tobacco containing an unusual quantity of foreign matter, or any crude tobacco, or any tobacco which is damaged to the extent of 20 percent or more, or any tobacco infested with live tobacco beetles or other injurious insects, or any wet tobacco, or any tobacco that contains fat stems or wet butts. The nondescript group is designated by the letter “N”.