Example: The clue is "places 4" and the guessers choose 1 correctly and then 1 wrong answer, but they had achieved consensus about 2 others (and are confused about only the remaining 1). So the turns ends but they inform the clue giver to inflate by 2 next turn. That clue giver (after the other team goes) will then say the clue is "people 5" and the guessers will know that they shall select 2 places and 3 people.
This can cascade beyond just a pair of turns.
Important: the clue giver cannot acknowledge the instruction during gameplay. That would certainly extend beyond giving a clue! The guessers must know that their clue giver can play this way prior to the game commencing.
Edit: I just consulted the rules and this is the most relevant section:
> If you are a field operative, you should focus on the table when you are making your guesses. Do not make eye contact with the spymaster while you are guessing. This will help you avoid nonverbal cues.
> When your information is strictly limited to what can be conveyed with one word and one number, you are playing in the spirit of the game.
The author's use of the pronoun "you/your" switches from field ops in that first paragraph to spymasters in that second paragraph, confusingly. With that in mind, it boils down to this: field ops cannot seek non-clue information from spymasters, and spymasters cannot convey non-clue information. The strategy I'm suggesting involves neither!
You really just need an algorithm to generate unique sets of 8 or 9 from the whole board, and identifies those sets by a word.
Of course, I never play this way in my own games
There's also all kinds of not necessarily intended communicaton from the guessers in the fact that you can listen to which words they were considering and didn't pick. Nothing in the game attempt to say that you should not consider, say, whether they were going in the right or wrong direction in their guessing, but it sure can make a difference in how to approach later clues. If they were being very wrong, there might be a need to double up on words that you intended, and that your guessers missed.
In the same fashion, nothing in the game saying that I cannot listen to those guesses as a member of the other team, whether guesser or spymaster, and then change behaviors to make sure we don't hit words they considered as candidate words without very good reasons. Let them double dip on mistakes, or not make their difficult decisions easier. It's not as if the game demands that everyone that isn't currenly guessing should wear headphones to be sure they disregard what the other team says or does.
The rule on giving clues is:
"If you are the spymaster, you are trying to think of a one-word clue that relates to some of the words your team is trying to guess. When you think you have a good clue, you say it. You also say one number, which tells your teammates how many codenames are related to your clue." (emphasis mine).
The rule states that the number should be the number of words related to the clue. There is later provisions allowing you to use zero and infinity, but outside of these carve-outs (and imo the "allowed" language is telling here, since it implies any other number not equal to the number of words is not allowed) I don't think this is legal.
Taking this a step further, given that it's well-known that a clue is deemed invalid when it pertains to cards in certain non-definitional ways (sounds-like, number of letters, etc.), it seems extremely reasonable to call a clue followed by N invalid if it doesn't pertain to N cards in a definitional way.
Another thing the guessers can do if unsure about one of the tiles from the last round, is to tell the clue giver which tile they think it was. The clue giver then tries to give a clue that either tenuously links to it or clearly excludes it. That can give the clue more scope for linking to several other words. It risks giving information to the other team though so is more of an final turn play.
Doesn’t the turn end if you hit the opponents word?