♦ *4NT is the Norman Convention and 5 shows an ace and king or three kings.
Only two pairs out of 32 reached (and made) this excellent slam in a major tournament. One reason was that the slam is extremely difficult to reach after a 1 ♠ opening. And many top pairs now favour showing a five-card major straight away.
This was a victory for the Acol style of bidding, where it is mandatory to open with the lower-ranking of equal black suits, for the reasons discussed over the past few days. All other pairs played in 3nT, making ten or 11 tricks.