Sorry about the delay but I went to see my son and his family in Oxford for a long weekend and actually played in the above event while at their home..
Board 1 was something of a comedy of errors.
Three pairs, including one from the team at the top of the table, bid a small slam on this hand despite having two quick losers in spades! One pair ended in 6 diamonds and two in 6 no trumps. 1st error.
Against 6 diamonds, however, after the auction 1C - 1D - 1NT - 2H - 3D - 4N - 5S - 6D West failed to find the spade lead and the contract was made with an overtrick. 2nd error. The bidding suggests that North/South do not have a spade stopper and a spade lead may be a good idea. My computer bridge program Jack correctly realises this and leads a spade. Somewhat surprisingly, he choses to lead the king of spades for reasons which are not apparent to me but any spade lead would do against 6 diamonds.
Against 6 no trumps by North, one East found the lead of the ace of spades and East/West took the first five tricks but the other East led the jack of hearts and the declarer made their contract. Only 12 tricks were made, however, despite declarer having 5 club tricks, 5 diamond tricks and 3 heart tricks off the top! 3rd error.
My partner, playing North, played in 3 no trumps after the auction 1C - 1D - 1NT - 2H - 3C - 3NT. Not surprisingly, he received the two of spades lead (the unbid suit) and was all set to go down but made 12 tricks when West switched to the seven of clubs after taking their king of spades! 4th error. West can tell that the two of spades is not a singleton since North would then have four spades which they would have bid after 1D or possibly 2H. It can't be from a small doubleton since they would have led their higher card so it must be from a 3 card suit. With normal leads the 2 would promise an honour which must be the ace. ( Even if it is from 3 small then North is left with a singleton Ace and a small spade return is safe.) As I said, a comedy of errors.
So much for the errors, lets see how to avoid bidding slams when the opponents have two quick tricks off the top. When I was first taught cue bidding I was taught to cue bid aces first and then a second cue bid in the same suit by either partner would show the king. In this system you can't show the king unless one of the partnership cue bids the appropriate ace. I now play the Italian system where where you cue bid aces or kings, singletons or voids, in cheapest bid order and the ideal is to only make a key card asking bid when you are certain that you don't have two quick losers in a suit. Lets see some examples.
The auction starts 1NT - 3S showing a game-forcing single-suited hand. West can now bid 4C as a cue bid since 2S said 'we are playing in spades'. 4C says 'I have first or second round control in clubs and am interested in a slam'. (With a minimum hand, short in aces and kings, West should bid 4S directly.) With this hand, East has no worries about two losers in any suit and could immediately ask for controls. He could do this whatever suit West bid and whatever system of cue bidding they are using.but playing the Italian system then over 4C East can bid 4D showing his second round control. When West bids 4S East knows that they are missing the king of hearts. He would continue to ask for key cards with this hand but with that extra bit of knowledge about partner's hand.
Now suppose East has Qx in clubs. The 4C bid is just what East wants to hear. Partner has the ace or king of clubs (not a singleton or void since they opened a no trump). East's two quick losers can be taken care of so they continue as before. If, however, West bid 4D then in, addition to to showing the ace or king of diamonds they are denying holding the ace or king of clubs since with the ace of diamonds and the king of clubs you would bid 4C, the cheaper bid, rather than 4D. It is this featur that makes the Italian cue bidding system so powerful. Holding two cards in clubs then, after a 4D bid by West, East knows with absolute certainty that they have two losers in clubs and must settle for a game contract. If they were cue bidding aces first then nothing woud be known about the king of clubs.
Note that the Italian cue bidding system does not necesarily locate first round controls. You must also use Blackwood or some such system to ensure that you aren't missing two aces!