Hi @magpie, welcome aboard to the forum.
Just a quick question, how do you know that the speed of the car on the speedometer was over reporting the speed?
If you used a GPS to try and calibrate the speedometer, this may not be the most suitable way to check the speedometer accuracy. This other thread covers this:
From what I understand these are parking senors and work when the car is either in reverse or when the sensors are manually activated by hitting the button on the centre console…
Does the senor work under both these conditions…can be checked by someone else outside the car and moving towards the sensor(s) in question.
