Dealership sold me car with mileage but is now asking me to sign a new bill of sale with mileage exempt. Should I sign it? Is this sketchy?

Update: It's a used car, so it has 100K miles on it, and that's what the original bill of sale says. I understand that if it has that kind of mileage, then the car is automatically "exempt." I guess I'm wondering, if that's the case and they both mean the same thing, why does it matter that I sign... show more It's a used car, so it has 100K miles on it, and that's what the original bill of sale says. I understand that if it has that kind of mileage, then the car is automatically "exempt." I guess I'm wondering, if that's the case and they both mean the same thing, why does it matter that I sign a new one? How does that benefit them? Will that negatively effect me?
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