What would 3H be in this auction? There should be an “other” choice.

Very strange. What do we think is going on? Does RHO hold 9 diamonds to the K and is planning to pull to 2D?

I already addressed your first two points, and I hope you have some evidence for your third point.

GIB works by creating possible hands for partner and opponents to hold on the bidding and figures out the best move from there. While on this hand 2♠X would score better than 3♦, perhaps if you held a more likely weaker hand you only beat 2♠ one trick, in which case 3♦= is better. And it is your fault you did not get to 3NT, you can always show a strong raise with 3♠ and the GIB would probably bid 3NT with a max and a stopper, or else you could at least stop in 4♦ if your partner has a min. A direct 5♦ seems completely unwarranted. Perhaps if pard had bid 3♦ directly you could, though I would still at least probe for 3NT with 3♠.

May I suggest not using all capital letters, as well as using the buttons for suit symbols?

I assume 2♠ shows 6+. If you ruff and cash the ♦A, your partner's card should tell you which minor suit to return.

Actually, this gives up an over trick against QJxxxx, Q, Kxx, Axx with South. So discarding seems better.

Law 7A: When a board is to be played, it is placed in the centre of the table until play is completed.

Law 7D: Any contestant remaining at a table throughout a
session is primarily responsible for maintaining
proper conditions of play at the table.

Based on Law 7D, all players are responsible for making sure procedure is followed. However, whoever switched the board directly acted against Law 7A. I would treat all the players as if they were in error, but whoever switched the board more so.

Realistically, the first player to draw their hand is the one least able to notice the error, the player who switched the boards when there was one hand missing the most able to notice the error, and the other two players somewhere in the middle.

If the first player to draw their hand and the person who switched the boards incorrectly were on the same side, I would call it a wash. Penalize both sides equally or give both sides average scores on both boards. If the first player to draw their hand and the person who switched the boards incorrectly were on different sides, AVG+ to the former's side on both boards and AVG- to the latter's side on both boards.

Give declarer whatever number of tricks he can make double-dummy after starting with ♥AK and seeing the ♥Q fall, or however many tricks he made (with the revoke) plus the 2-trick penalty, whichever is greater.

Gotcha.

1S-2H-3C-3D-4N-6D

1C-1H-1S-2D-3C-3D-4D-4H-4S-4N-6D

Even though I've only discussed Kokish with my partners through 2♣-2♦-2♥-2♠-3NT, it logically extends to 2♣-2♦-2♥-2♠-5NT to show this hand. Then partner is forced to 6NT or can show a long suit at the 6-level.

How about post-it notes on all boards that will be played by the bumper pair saying, for example, “NS5 do not play. Bumper round”. I think there would be even less of a chance for people to miss it then.

Here is the ACBL law regarding claims not addressing outstanding trumps:

C. There Is an Outstanding Trump
When a trump remains in one of the opponents’
hands, the Director shall award a trick or tricks to
the opponents if:
1. claimer made no statement about that trump, and
2. it is at all likely that claimer at the time of his
claim was unaware that a trump remained in an
opponent’s hand, and
3. a trick could be lost to that trump by any normal*
play.

To figure out if 2. is true, I would want to see the whole hand and how it was played. Maybe there was a bad break in drawing trumps that declarer didn't notice.

What suit is trump? Who is the declarer and who is the dummy? Who are the defenders? Some necessary information is missing.

First the Jack of Spades. If trumps break, club to the Ace and club back. If trumps don't break, heart to the King and ruff a diamond.

As usual, poll options should partition the universe. It seems like you didn't see the crossruff line?

For me, 1430 is just the default. Like Michael, 90% of people I know play 1430. When the opponents bid 4N I ask “1430?” and they say “yes” most of the time. If you are already going to play 4N as “ace” asking, then you might as well play the most played version. Kickback is played by much fewer partnerships around here though. I would never assume kickback undiscussed, but I would assume 1430 undiscussed with a good partner every time.

WIn in hand and play a spade toward the ten. I'm trying to find a second entry to the dummy to lead hearts through East twice. Fall back on clubs 3-3. If East wins the ace and plays a diamond, discard a club.

With any hand of 10+ points, start with a double.