Are you familiar with any similar cases/circumstances re the admin error?
Yes. The issue, of course, is whether adequate checks have been made to ensure there are no errors outstanding.
there is a significant difference in his breakdown of scores
I can understand why you are suspicious, but there's no such thing as a totally reliable reasoning test, and it's perfectly possible for scores to fluctuate. My own LA administers two VR tests of equivalent standard. Some children will score 120 and 120. Others will score 120 and 110! NFER have described such tests as a 'snapshot' on a particular day.
don't want to get school's back up by reminding of them of their error...
It would be entirely reasonable to ask questions at the hearing ("What checks have been made to ensure there are no remaining errors?" "Why haven't the answer papers been kept in case something needed investigating?).
Parents have one year after an appeal to take a complaint to the ombudsman. I would have thought the ombudsman would expect all the evidence to be retained by the school up until that point in time.
Even if we are successful in illustrating ability, places are of course now fully allocated.
Arrangements can vary, but in most areas appeal panels consider non-qualification and oversubscription issues at the same hearing.