3♠: GF splinter
3NT: This bid was slow, like 1-1½ mins. N later explained that he had forgotten if 3♠ was nat/weak or a splinter and was trying to remember. His written explanations to E supported that. In the end he decided to bid as if 3♠ was a splinter.
4♣: Cuebid. The committee decided that S's hand had so many extra values that pass was not a LA. So 4♣ was a legal bid whatever UI were present.
5♦: Weakest possible action at that point, according to NS's slam principles.
6♦: The committee decided that pass to 5♦ was a LA, since 6♦ was a quite aggressive bid.
6♦ made. N had a pretty decent hand for his bidding, so the slam was good, like 75% or so.
Some might well argue that 5♦ was an underbid.
Is 6♦ a legal bid, given these committee evaluations of N/S's hands?