This mileage thing is interesting. We have bought a car that had 12000 Kms on the CT certificate in 1999 and has 13500 now. The car is 47 years old. It was bought initially by an old couple in 1972. They ran it till ill health stopped them and it sat in the shed. They passed away, and the house remained empty for 14 years when it was sold to a Brit in 2004, and the car was still in the garage and came with the house, and he did nothing with it till he became ill and gave it to a pal before he died in 2014. That pal has had the car 5 years and has now sold it to us. So in 47 years it only worked for a little old guy in a little village for 8 years. Since then it has done1500 kms. So these low mileages are possible.
My other R4 has 150,000kms on it. It was the truffle mans car, and he used it to drive round to farms collecting truffles and selling them on. It is a 1985 car so is 34 years old so 35 into 150k gives 4285kms per year or a little less that 3000 miles pa. Again, a very low mileage, again confirmed by paperwork.
So it could be that the mileage is just what it says. people only used the car to go to church, or the odd trip to somewhere, they did not use it the way we do now.