The best way to know your cylinder bore (diameter) is to measure it. There were markings that did apply when the cylinders were new, but it is over 20 years and you do not know the history of the cylinder, like if it has been replated or not.

If the cylinder is damaged and the lining is not repairable, then it needs to be replated. When you get it replated, you will usually send it away with the new piston and they will get the plating/piston within tolerance.