You have mentioned that there is a covering letter dated 1/11/1999. This letter will show that the cheque was drawn or issued more than 6 months back. To attract s.138 NI cheque should be deposited within the period of validity which is 6 months. In this case there is evidence to show that the cheque is a stale cheque and therefore according to me S.138 will not be attracted. Please note that the date which the cheque bears is the date of drawing only so long as there is no contrary evidence. In this case there is evidence to the contrary in form of covering letter dated 1/11/1999. Therefore even if a date is put on the cheque as of today that would not be the date of drawing.
I am emphatice S.138 would not be attracted.