Ew, not so cool then. I guess my thought is that if you're getting inspected annually or semi-annually, why would you need to pre-buy mileage then? Go to your annual inspection, read the odometer, pay the tax, get your plates for next year. Cheaters will always cheat. A guy local to me went 4 years on an expired registration, he was finally caught and his fine was less then what he would have paid for being legal.
I understand the difference between sweet vs sour crude. Sour crude is high in sulfur, sweet is low in it. The high sulfur requires additional steps at the refinery to be used as fuel, think ultra low sulfur diesel (ulsd) fuel. Some other uses for crude oil don't require the sulfur to be removed, so sour crude will be used for them and processed at the refinery for them, whereas your sweet crude will be shipped to a refinery that produces motor fuel.