The math to figure the mileage adjustment is the number of months since Sept 2015 X 1042, then you subtract your current mileage from that.

So, if you turn in your car in December of 2016 (for example), your calculated turn in mileage is

15 months X 1042 = 15630

24300 - 15630 = 8670 miles, using the look up table from the settlement

https://www.vwcourtsettlement.com/en/docs/FTC_Consent_Order/Attachments/Attachment 2B.pdf
The adjusted mileage range is 5,001 - 10,000 for an amount of $3,090 that is added to your buyback amount.

The next lower mileage range is 0 - 5,000 for an amount of $3,660, a difference of $570 additional amount that could be added to your buyback amount.

Since your car is low miles, and you cannot go below Zero (0) miles for the adjusted buyback amount, you could sit on your car (and not drive it) for an additional 4 months, to get the adjust mileage to 4502, and move down to the 0 - 5,000 mileage range, Gaining you an additional $570 buyback amount.

Once you get your cars adjusted mileage into the 0 - 5,000 range, you would just need to drive it less than 1042/month to keep it that range.