I can’t imagine that they even look at it until the 3 years is up. The limit is 60,000 miles over 3 years. I suspect that the mention of 20,000 miles a year is just for ease of understanding, rather than something that they police. If you think about it, they wouldn’t charge at a year point, as you may be well under the next year and still meet the 60,000 over the 3 years.