I'm sure you know deep down, just as I do that they will have used this in an illegal fashion during this season but it can't be proved. Clever on Red Bulls part in one sense but this sort of thing goes beyond 'bending the rules' to just flat out breaking them in the knowledge no one could prove you did it, which goes beyond any notion of decent sportsmanship.
Again they don't have to prove they used it, they didn't or couldn't prove BAR ever ran underweight. They had the facility to run underweight even though do so would mean the car wouldn't run. BAR even proved that at no time they could run underweight.
It didn't matter, because they had the facility to, they got a 2 race ban.
Red Bull or the FIA don't need to prove if they used it. It shouldn't be there anyway according to the rules.
2 race ban should be the minimum. After the BAR fiasco the fia stated they would come down even harder on this sort of thing to deter out right cheats.
It just shouldn't even be there as an option. They don't have to prove anything.