of course the euro test could indeed be entirely fake, like the moon landing
Well, for our purposes, it is. It won't have been carried out with the tyre mounted on an Omega. To be honest, I wouldn't be surprised if it wasn't carried out on a real car at all, but a test rig in a lab.
Road surface, weight of the car, suspension geometry and damping characteristics will all have an effect. As with most things, dumbing something down to an "A" rating actually removes any useful information from the equation.
Just like our dishwasher. A rated, so really good, then.
...except that it doesn't get anything clean if you use it on the economy programme on which the A rating is based, so I manually select the 70 degree C "pots and pans" programme every time, otherwise I might as well fill the bowl and get my marigolds on.