In addition to the results from the test bench, you need to provide a completed form with the physical and chemical properties of the oil, including the result of the infrared absorption spectral analysis.
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JASO can also carry out market surveys of classified oils present on the market and, if non-compliance is found, ask the applicant for explanations.
In the case of Japan (and perhaps some other countries as well), JASO may also take legal action based on existing national laws.
This is true for a significant portion of the products marketed. E.g., in Europe, the conformity assessment and 'CE' marking system that I am familiar with is also predominantly based on self-assessment. Obviously there are mechanisms for checking compliance by authorities.
The situation is similar with the engine submissions to the EPA discussed on this forum. This, too, is a system based on self-assessment with mechanisms for checking by the authority and the existing possibility of penalties.
The difference, of course, is that oil labeling/rating is voluntary and, for example, the Japanese organization has little ability to act outside Japan. CE and EPA, on the other hand, are mandatory with sanctions enshrined in national law.