Same Hand, Different Line

K Q 9 7 6
A K 7 2
A
10 9 3
A 10 5 4 3 J 8 2
Q 9 6 J
5 4 3 10 9 8 7 2
Q 4 K 8 7 6
------
10 8 4 3 2
K Q J 6
A J 5 2 Contract: 6 hearts

Well, two more declarers made 6. I had to go through their play to see who made a goof and where. Here's the first (and tamer) case. Opening lead the queen of clubs, two rounds of hearts, getting the bad news, cash the ace of diamonds, ruff a spade to run three diamonds, sluffing two clubs and then both declarer and LHO sluff a spade on the fourth round. Again, West didn't wanna ruff in and get out with a club. And again, I hafta point out that declarer has already sluffed all he needs to, the king of diamonds (which this declarer played last) is a winner that you can capture, and you're not giving him anything in ruffing it out.
Hey man, he can only ruff two clubs in dummy and he has three little ones. How do you think he's going to get rid of that fourth club?
Well, anyway: it was substantially the same. Have you counted? Well, there have been 8 tricks thus far. The 2 of clubs was ruffed, the queen of spades was ruffed, the 5 of clubs was ruffed as West again threw a spade, the 9 of spades was ruffed drawing both the ace of spades and king of clubs as East chose to save the 10 of diamonds. That's 12 now. And now the queen of trump captured the last trick.
Here is what the other declarer did:
Diamond to the ace, spade ruffed, two diamond leads, sluffing clubs, of course, ace of clubs, ruff a club, ruff a spade, lead a club. This declarer evidently didn't want to test for a 2-2 heart split, which would make the slam a laydown, an overtrick possible on a favorable location of the ace of spades. Anyway, on that third round of clubs, West went up with the 9 of trump and declarer ducked. The ace of spades was now led, and the rest is history. Declarer ruffs, draws trump and has a good dummy with the king of spades and 7 of hearts. He had ruffed only one club.
Here is what the hand looks like after declarer ducked that 9 of trump, sluffing a spade:
K Q
A K 7
------
------
A 10 5 J
Q 6 J
------ 10 9
------ K
------
10 8 4
K
J

And it appears that this is it, that West cannot do anything now to beat the contract. A high spade (as was led) allows declarer to ruff, draw trump and claim a good dummy. A low spade allows declarer to sluff the J of clubs, cash two rounds of trump, ruff a spade and cash the K of diamonds. A heart lead allows declarer to draw trump in two rounds, ruff a spade, cash the K of diamonds and ruff a club.
Suppose West doesn't ruff that third round of clubs? Lemme see. Declarer must ruff, so the hand would look like this:

K Q 9
A K
------
------
A 10 J
Q 9 6 J
------ 10 9
------ K
------
10 8 4
K
J

Wherein, hm-m-m, lemme see. It looks as though declarer could be beat.
It would appear that the three declarers made opposing mistakes that amounted to the same thing. The first two made the mistake of not capturing that fourth round of diamonds, a clear winner, and by the luck of the cards, wound up capturing nothing from declarer. The third defender, on the contrary, spent his natural trump trick, on a low club. Of course it was actually the 9 that West spent, but when declarer ducked, the queen could now be picked up, so it amounted to the same thing as spending his queen on a low club while his confreres declined to spend the queen on a clear winner!
The lesson in reference to ducking declarer's clear fourth-round diamond winner is discussed here (at the end). And the lesson in regard to the third declarer was just given above. You don't wanna spend that valuable trump on nothing.