I tihink the FIA wanted an independent voice to adjudicate on the meaning of the rule as they didn't want to be dragged through endless appeals, not because their was any confusion. The tribunal agreed with their opinion, so there was no evidence of the FIA not knowing their rules as a result of the tribunal.
Mercedes didn't exactly say that the FIA didn't know its own rules. The fact that they didn't only emerged as a result of the dispute - Mercedes didn't prosecute themselves. The FIA could have said "we're not going to prosecute because tyre testing under the direction of Pirelli is not track testing under Article 22.1" and then they could have requested Pirelli to offer suitable testing opportunities to all the other teams on a fair and equitable basis forthwith.
It didn't add anything either.
Whilst it may be fair enough to call my observations about the FIA a "rant" it doesn't detract from the baselessness of your accusation (you were the one who brought this up) that Mercedes undermined the structure of the sport for a short term competite advantage.
Questionable technical things are normally run past Charlie in advance (that being an actual part of his job, whereas deciding when a test isn't a test is not). The other teams are free to look at cars, too. That's why they quite often see things on other cars and ask for clarifications.
The Red Bull is indeed available at race meetings to be scrutinised by the scrutineers, but the other teams can't scrutinise the Red Bulls. Furthermore it doesn't constitute advanced notice of Red Bull's intention to run any questionable or flat-out illegal components. The FIA only finds out about these things, if the scrutineers spot them, during scrutineering (i.e. not in advance). The other teams only find out about the arguable or illegal components once Charlie has said to Newey "I say, old bean, would it be too much trouble to fix this little problem by the next race?" and then put up a notice about it in the paddock, if he even bothers to do that which he doesn't always.
As was proved - they gave it their best shot, though.
The Mercedes test was more transparent than that, since the Mercedes transporters etc were there to be seen by the other teams, not leaving the circuit, not packing up, on Sunday evening and Monday after the Spanish Grand Prix, so every team principal in F1 must have known something was up at least two days before the test ever happened. There was certainly no question of the other teams remaining in the dark once the test had been carried out - it is simply not possible to test for three days at the Circuit de Catalunya without the other teams knowing.
There's a difference between doing something in the belief that the rule says you can, and asking for permission to do something, being advised that you can't but that if certain conditions are fulfilled then it could possibly be acceptable, then deliberately not doing the things you were told might make it OK, then blaming the people who offered you friendly advice for saying it was OK.
And I would caution against relying too much on the intention of the test ban as part of your argument, because I could just as easily bring up the intention of the rule that says a car's floor must be impervious, or the rule that you can't keep changing engine maps all the time, etc. No team can afford to be exclusively concerned about what the regulation was intended to mean, and they have to consider what the regulation actually says and to look for ways of interpreting that in the most advantageous way for themselves.