The date is stamped into the steel on the outside part of the wheel as they were positioned on the axle from the factory. Look closely, and you will see it. There is no definite correlation between that date stamp and the date that the tractor was manufactured. However, it will give you an approximation. Who knows how long the wheels were sitting in inventory after being manufactured by the vendor. The only definite conclusion that can be drawn is that the tractor was manufactured AFTER the date stamped on the wheels (assuming that the wheels are original to your specific tractor). I have been told that Yanmar did not keep records to tie a serial number to date of manufacture. Sounds strange to me, but I can only go on what I have been told by those who have been directly involved with Yanmars for many years.