I beat you.Just want to mention that, um, remember the year 2000 problem? Any numbering scheme that uses the year really should have all 4 characters. Corporate America spent billions fixing that problem between about 1995 to 1999. Many uninformed people think it was a problem that didn't happen, but actually it was a real problem that was fixed in time because most mainframe programmers (like me) dropped everything and worked on that for 4 or 5 years. Not what I would call productivity!
I dealt with an inventory system that had a SINGLE digit for the year.
As a user if you saw 4, you did not know if it was 1974, 1984, 1994
The system was designed WAY BACK when memory and storage were EXPENSIVE.
It was also designed back in the era when the industry expected to replace programs every 5-10 years. So a single digit year was not expected to be a problem, as they expected the system to be replaced before 10 years.
NO ONE expected that system would still be running 30+ years later.