When I was looking at used trucks last year, I found one where the mileage displayed on the odometer was like 150,000 but when I did a carfax, the maintenance record showed MUCH higher, like twice as much. When I pointed this out to the seller, he insisted that the odometer was correct. I passed.
I had a gauge cluster go out on a 2003 Silverado. If memory serves me right I took out the cluster and got a new one from Chevy. They asked what the mileage was so they could enter it into the new one. It seems I could have said anything.