There's a few things to rule on here. I don't feel terribly hard done by on the ruling we received at the table, but am curious whether in a more serious event things might have gone differently:
Match pointed event.
In case relevant, E/W play regular Landy.
1N was announced as 15-17 - but their agreement was in fact 12-14.
In the play, I (W) got 8H lead, won in hand, and 'knowing' the QS was with S I played to the K and ran the J hoping to drop the 10. When it lost, I asked again about 1N, N repeated 15-17, and S now corrected him. We called a director, who told us to play it out (and reprimanded S for correcting her P during play).
In the end, he transferred the trick back to me, and observed that, had we known it was weak, we might have bid to either 3N (making) or 4S (going off), and since we couldn't know which, he'd leave the result as it was. I said that seemed pretty reasonable, but looking at the hand afterwards, I felt that E bidding 4S (when 5 has shown 5+) is a bit of a stretch.
Since I think overcalls of a weak NT should be constructive (so you can find game), on the E hand, I think I would personally have blasted 3N had I known S had a weak NT. Even if you content yourself with 2N, it makes the same number of tricks as Ss, so we would have got a better score.
How would you rule, given all the uncertainty? In general how optimistic a view of their competence/luck are the victims of an infraction entitled to?