That headline may sound like a truism, but the truth is one grade of cotton cannot be substituted for another when it has low staple or strength or color. That’s what O.A. Cleveland says the Chinese textile mills are finding as they try to spin cotton that has been held in its reserve for four or five years. Deteriorating cotton generally has to be mixed with higher grades to avoid problems with yarn production and that may require the Chinese to import more cotton from overseas.