The Redouble Used and Not Used

10 9 8 4 2
Q 10 8 4
A
7 6 2
A Q J 7 3 K 6 5
9 6 5 2 A K J 7 3
10 9 5 6 2
9 J 8 3
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K Q J 8 7 4 3
A K Q 10 5 4 Vul: Both

A freak hand, but would anyone doubt a reasonable chance for slam, particularly when you can offer your patner a choice of suits? It would have to be, well, an equally freak distribution around the rest of the table to defeat slam here. So what's the problem? Well, it wasn't an absence of slam bids. Only two bid the grand, but I'm not here to criticize the rest. It's awfully hard to convey the ace of diamonds to South, or conversely, for North to fathom that that's about all his partner needs for grand. No, it was the absence of those who didn't have enough confidence in their chances to redouble, particularly the three in five clubs. You can foresee three losers here? You've gotta work at it.
First the good employment of a redouble: one pair got doubled in four clubs! This was redoubled. Quick, now: where do you suppose they finished in the standings? Ah, you got that one did you. No, they didn't beat the two in grand slam, though they lost to an undoubled grand by only 20 points! But they beat everyone else for third highest!
As covered elsewhere, I think it's primarily a matter of not knowing how to score, so let me first take those of, well, greatest culpability, the three in 5 clubs doubled.
If you redouble, you'll beat those in slam. If you don't redouble, you don't. You beat 'em only if there are but 11 tricks on the hand, where the redouble wouldn't hurt, and you would be hurt only if the hand will yield but ten tricks! So let's look at the score: Little slam vul (minor suit) will give you 1370 points. The same 12 tricks with a redouble of a five bid yields 4 times trick score, plus game bonus, plus 100 for making a redoubled contract, plus 400 for the overtrick! It's gotta look like more than slam right away, but lemme add this up. That's 400 + 500 + 100 + 400, which looks like 1400, huh?
Those who were doubled in little slam would pick up, on a redouble, 480 (4 times trick score) plus 500 game bonus plus 750 little slam bonus, plus 400 for the overtrick, plus 100 for making a redoubled contract. That's, hmm-mm, surprise! More than the grand. I hadn't worked it out before. That's 2230, while a grand brings in only 2140. And you're a trick safer than in grand!
Lemme look at 4 clubs redoubled a minute: that's 320 for trick score, 500 for game score, no slam bonus, 100 for the redoubled contract and 1200 for the overtricks, for 2120. Not half bad, but as mentioned, a little short of the grand.
Incidentally, if you find that too much figuring to do in the moderate haste of play, you might find it easier just to figure the difference. On a redouble of 5 clubs, the redouble increases the trick score by 300, an overtrick by 380 (i.e., 400 minus the 20 you'd get undoubled), and you get 100 for making a redoubled contract. That just beats the 750 little slam bonus, plus giving you a one-trick cushion if the hand doesn't jell as expected. Not bad, not a bad opportunity at all. And those doubled in 6 clubs? Well, they'll increase their trick score by 360, an overtrick brings 380 more, which is 740 right there, and adding 100 for making the redoubled contract brings you beyond the 750 in slam bonus you give up. So they could have beat the people in grand though not the pair that got doubled.
How do the people doubled in 5 fare vs. the grand? Well, they don't beat that. They would give up a 1500 slam bonus, which is too much to overcome. They would pick up 300 in trick score plus 760 on two overtricks plus 100, which falls way short vulnerable. Still, they'd beat everyone in 6 clubs, as mentioned above, and if they're willing to settle for 5 on that hand, they presumably aren't giving serious thought to grand slam anyway and would do well to redouble.
There is one more factor that must be faced here, namely that the opponents might have second thoughts on a redouble and decide to sac. Here they had a heart fit as well as a spade. They would get bad breaks from the same distribution that allows N-S their grand, but it looks to me not so bad that they couldn't beat even an undoubled little slam, much less a redoubled one. So we're not here to say it couldn't happen; only to say that there are golden opportunities when you get doubled on your way to slam or even in little slam if you're thinking grand, while conversely, if you let an early double stand (before a slam bid) without a redouble, you'll often find you've been suckered into a poor board..