@Alligator You could include dates, IF the dates would be meaningful information for you later. Otherwise, unnecessary work. If I'm dealing with a numbering scheme, I ask questions like: How big could these numbers get? If I can get away with two digits, that's better than having to use four each time. I also ask, What information do I want to get out of just looking at the number? (Maybe the year is useful after all.) Another question: Can I pre-assign certain numbers? When I did survey research, we coded "don't know" as all 7s, we coded "no answer" as all 9s.