If a cop nabs you at 111kph, 99 times out of 100 your own speedo is likely to be reading over 110kph so fair game. I bought my car brand new 3 months ago and I had Snapchat open (as the passenger obviously.....), swiped to the speed filter and with my speedo bang on 100 it was reading 95.6. Quite frustrating really, I would much prefer my car to go exactly what it says I'm going.
Car A could be going 99, Car B could be going 95, and both speedos read 100. 4kph is quite a big difference if you're on the motorway and potentially holding people up.