This occurred at the club last night. West and South are experienced regular county B-team players, East occasionally plays for the C-team, North is considerably less experienced. NS are a relatively new partnership, and have been playing together once a week or so for several months.
2♠ = weak two
X = takeout
2NT = Lebensohl (not alerted)
South announced at the end of the auction that 2NT should have been alerted, that it was Lebensohl. West was not minded to reopen the auction, and the hand was played out.
Result: 5♦(S)-1, NS -50.
West asked South why he had bid 4♦. South replied that he had a weak hand with six diamonds and couldn't stand 3NT. When West suggested this auction usually shows a strong hand, stronger than an immediate NT overcall (say 19+), South said they play 2NT as 17-20, and that it was not likely that North had a stronger hand than this. Under "defence to weak twos" the NS convention card had "X = takeout, 2NT = Lebensohl (0-9)" There was no mention of a range for NT overcalls, not on the CC, nor in several pages of system notes.
If called as director to give a ruling, what would you do?