Didn't mean to say they are the same year to year. As we pointed out, the serial number is used to track changes, such as the seat, addition of a cupholder, changes to "power on" fuel system, and so on. The 2004 and 2006 have a bunch of differences. When a customer needs parts, the serial number tracks all the changes model to model. The difficult part for a dealer is the communication of model year to a customer. A dealer can recieve a tractor in June, sell it as a 2009 in July, but the serial number would track to a 2008 production run. This isn't unusual at all.
When there are changes, most of them are pretty subtle...except the cupholder.....it's easier to point out what you have. The 20S was designated differently since the engine and transmission were completely re-done. It really is a different tractor than the 20.
The production year on KIOTI Tractors is coded by the first character in the serial number. The "model code" is the next 3 characters in case there are engineering changes/updates during a production year. The rest of the serial number tells you where you were in line.
For this type of equipment, the hours on the meter is usually the most important thing to look at. The "year of the tractor can be mis-leading.