Mileage Discrepancy HPI check Advice

[OctaneV8]

Looking to buy a car, all service history and MOTs show steady increments on the mileage, no big jumps except an HPI check shows mileage going from 49,000 to 490,000 a few years ago - subsequent years of MOT cert mileage shows 52k, 60k, 70k etc. so this looks likely to be a typo, by an MOT tester perhaps?

Anyone had any issues with this before? Any "side-effects" to be concerned about?

Just put a deposit down on a private sale and due to pay in full and collect tomorrow. Please share if you've had a similar experience. Thanks

[OctaneV8]

After using the search function it sounds like it is worth just clearing it up with a letter to the National Mileage Register (NMR) or apparently it "falls-off" after 4 years according to this:
http://www.pistonheads.com/GASSING/topic.asp?h=0&a...