Nickel plating - which is what O.S. uses in their liners, is not machined post-plating due to nickel plating very evenly. Only true chrome is ground to size post-plating due to uneven plating. That groove in the liner could have easily happened by a previous handler that turned the engine over with foreign debris that got inside the engine. Unless you bought the engine new from a retail seller, you do not know the exact provenance of that engine. Replacing the piston and liner with ASP parts will rejuvenate the engine and be much better quality and longer lasting than the OEM parts without question.