I type slowly so you can understand
You said the car was sold showing just under 47000 miles on the odometer. My guess would be that the figure was actually in KM's after coming over from Japan. Therefore the true reading in miles was around 29,000. They then changed it so that it was now clocking up in miles from then on. The numbers weren't changed - just the type of input (miles not KM's).
So, since then you have clocked up around 53,000 miles and are showing 100,000 on the odometer but that is a mixture of KM's and miles. Therefore, if you take the original figure of 47,000 and divide that by 1.62 you get the miles of around 29,000. You then add that to the extra miles ( 53,000) and you get 82,000.