your sons position on the waiting list seems to have quite an effect on whether or not your sons appeal succeeds
It would be unlawful for panel members to take account of where someone is on the waiting list, so it would be a matter for concern if they were in receipt of this information!
There's no reason why the panel shouldn't know the score, but only if it is in the case papers sent to all parties. (Parents and panel members must be given exactly the same information, or there would be grounds for a complaint.)
If information about the score is made available, then statistically it's probably correct that you stand a better chance with a score close to what was required. However, in theory there's no reason why lower scores can't succeed provided the case is strong enough.
75 appeals is a huge number, though!