Squeezed out of a Top Trump?

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

Six hearts. If trump split 2-2, the hand is a cakewalk. You'd be testing a ruffing finesse in spades for an overtrick. You would draw trump in two rounds, unblock the A of diamonds, go to the A of clubs, sluff two clubs on diamond honors, and ruff a club, then the K of spades, pushed through sluffing a club if uncovered, ruffing out the A if played second hand. You would then go back on a second club ruff in dummy and throw the closed hand's last club on the Q of spades. Oh, it wouldn't pan out, but your contract for 6 would be safe all the time.
But trump aren't splitting 2-2 and there isn't even a right guess for picking up the Q of hearts. Yet 21 people made six hearts here. Eighteen of 'em got the A of spades opening lead! Thanks a lot, fella. That do make it easy. Still, there were 3 who made the slam without the A of spades lead, and I decided to have a look at how they did it. A clever play by declarer? A boo-boo by a careless defender?
The first successful contract (without the A of spades lead) involved a defensive boo-boo. No, you can't be squeezed out of a high trump. But the sequence led to a situation that was an awful good imitation of a squeeze, as will be described.
Opening lead the 3 of diamonds. Declarer cashed the ace, king of trump, came to the closed hand with a spade ruff, cashed three diamond winners, sluffing two clubs and a spade, while West also sluffed a spade on the fourth round. That was his mistake that led to his downfall. The hand looked like this prior to the last diamond lead:

K Q 9 7
7 2
------
10
A 10 5 4 J
Q ------
------ 10 9
Q 4 K 8 7 6
------
10 8
K
A J 5 2

After the next lead when West sluffed a spade on the last diamond lead, the hand looked like this:
K Q 9
7 2
------
10
A 10 5 J
Q ------
------ 10
Q 4 K 8 7 6
------
10 8
------
A J 5 2

Now watch declarer's play and see if West can recover from that boo-boo. Cash the A of clubs, ruff a club, ruff a spade. West has to follow to each lead, and we reach this end position:

K Q
7
------
------
A 10 ------
Q ------
------ 10
------ K 8
------
10
------
J 5

Declarer leads a low club, and this is where what transpires looks an awful lot like a squeeze, even though the top trump is a key player. If West ruffs, declarer sluffs a spade, and now can crossruff out the last two tricks. If West instead sluffs a spade, declarer ruffs his club, ruffs a spade back, allowing West the last trick with the top trump.

Now go back to the seven-card ending above, before the fourth round of diamonds has been played and note what happens if West ruffs -- and gets out with the Q of clubs. The hand would then look like this:

K Q 9
7 2
------
------
A 10 5 4 J
------ ------
------ 10
4 K 8 7
------
10 8
------
J 5 2

Wherein it looks to be self-evident that declarer with 3 spades in one hand and 3 clubs in the other and two trump in each hand, cannot pick up either the A of spades or K of clubs, or in other words, having lost one trick to the high trump, cannot realize more than 2 more ruffs in each hand, after which four tricks, declarer will have to surrender one more trick for down one.
Is there a lesson here? I think so. One must guard against generalizing too glibly and as always acknowledge that there'll always be exceptions. But if declarer offers you a clear winner to capture, and you're either fourth hand or you're otherwise certain your partner can't win the trick, I'd say it's a good idea to capture that winner -- probably in the neighborhood of 95% of the time. I see it all the time that defenders hold off taking that trick, presumably with the expectation that they'll get it later. But often that opportunity doesn't come around again. Of course when you have a very positive reason for declining to win, as in denying declarer an entry to dummy, then be my guest.
West didn't lose his natural trump winner, of course. What he lost was the ability to get a winner with it. In the three-card end position, you see that West is either going to capture the 5 of clubs or the J, while his partner holds the K.