Fare codes with a N after them, e.g. Yn denoted night fares which were generally sold at a discount. They were usually available for flights that departed between 10:00 pm and 5:00am and are left overs from the regulated days. Yn was commonly referred to as "night coach". You would also see Fn. As discounted fare buckets were created they pretty much disappeared. I can't recall the last time I saw one.