Dont wish to be pedantic, but I provided some evidence and you lept to an incorrect logical conclusion.
But you could be right about Which? getting it wrong, noone is infallible.
In terms of reliability, though, which is what the original question was about. Which? do lots of surveys of their members (Joe Public) to gather actual breakdown statistics. So in this case they are probably right.
I have to declare a vested interest here, I am a paid up member of the Consumers Association.