does this not prove that the school can admit addition pupils without prejudice? If I used this information at appeal have I won my case?
Even if it did prove that they can take extra pupils, it will not only have proved it for you, but for all the other people appealing.
In other words, it's not possible for a panel to decide that for some appeals the school can take over PAN/IAN, but for other appeals they can't.
It is also likely that the extra in-year admission was due itself to a successful appeal - appeals can happen at any time or year.