What is the year of my craftsman model 917.2559101?

You can tell the year on a Craftsman by the first six digits of the serial number. They are in groups of two. First two digits are the month, second two digits are the day and the third two digits are the year.

Apparently this dose not work for all Craftsman Mowers. My model #917.255520 Has a serial number of 1631S37112 meaning it was made on the 16th month and 31st day of the year 20S3... I think..??