According to my knowledge and info:
S- The car is less than 12 months old from the first registration date and under 10,000km.
As good as new. The exterior and interior are in immaculate condition.
6- The car is less than 36 months old from the first registration date and under 30,000km.
The exterior has some very minor scratches/scrapes and dents. They may not need to be repaired.
5- The car is under 50,000km.
The exterior has some minor scratches/scrapes and dents. They may require some minor panel beating work and/or painting.
4.5 - The car is under 100,000km.
The exterior becomes a grade-5 car with minor repairs.
4 - The car is under 150,000km
The exterior has some scratches/scrapes and dents. They will require some minor panel beating work and/or painting.
The interior has some tears, cigarette burn marks, and/or stains. They will require some minor repair.
3.5 - The exterior has some noticeable large scratches/scrapes and/or large dents. They will require some major panel beating work and/or painting.
The interior has many tears, cigarette burn marks, and/or stains. They will require repairs.
3 - The exterior has many noticeable large scratches/scrapes, paint blemishes, and/or large dents. They will require major panel beating work and/or painting.
The interior has many tears, cigarette burn marks, and/or stains. They will require many repairs and/or interior parts will need to be replaced.