**Most have a 5 digit code stamped on them. From what I've been told (not my research) - here is the breakdown: ****First digit is the year. 8 would be 1988. 9 would be 1989. The next 3 digits a for the day of the year. 001 would be January 1st and so on. The last digit is either the printing/sorting location or the employee shift number. Location 1 or 2 vs. Shift 1 or 2 etc. So, in theory, digits before 90171 (January 17th, 1989) would have the FF error inside.**