I recommend taking a look at the TCA website, tcatrains.org. They have posted a comprehensive view of the grading standards in the public accessible section of the site. The familiar grading of C-1 to C-10 are physical condition and appearance only. In 2020 TCA adopted an additional set of standards for operability. These are O-1 to O-5. they are described on the website. Hope this helps.
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