Suzuki assigns a year letter code to the end of each model name. Perhaps you’ve noticed this letter designation in your Suzuki repair manual or owners manual but weren’t sure what it meant.

Here’s how it works: If you own a 1999 Suzuki TL1000S X or a TL1000R X or a GSXR600X etc the X at the end tells us it was sold as a 1999 model year. The year of manufacture is not necessarily the model year. Usually around October the new models are released, so it's possible to have a built date of say 10/98 and have an X (1999) model even though it was built in 1998.

You might notice that "I", "O", "Q", "U" and "Z" are missing from the codes. The letters I, O & U cannot be used in a Vehicle Identification Number (VIN) at all. The digit / number 0 and letters U & Z are not used in the year model code.

There is more VIN information here on a Wikipedia - Vehicle Identification Number page.