We are in Storm player turn.
Player starts a counter war, that they win. Then they switch to “solitaire mode”.

Thinking aloud, player quickly counts “so, we have played this…this…this… 5 spells total”,
then grabs a die to represent the storm count, and puts the die at 5.

Player miscounted. Storm count should be 6.

Should we intervene right away?
Opponent is obligated to correct Storm player?

Edited Francesco Scialpi (Aug. 6, 2018 01:07:57 PM)

I think, it is derived information, and we shouldn't stop him. List of spells - open, their numbers - not.

Edited Sergey Zinkovski (Aug. 6, 2018 01:34:27 PM)

Sergey, if you believe this is derived information you should interve : “Players may not represent derived or free information incorrectly”, MTR 4.1.

I believe this counter isn't part of the game (so it's not defined by "Free information consists of: The number and type of any counter that isn’t defined as status information.“ or status information ”Status information consists of: Counters a player has attached to them."), and since it isn't an object or the caracteristic of an object, it's not derived information. By default it becomes Private information which Storm player is free to represent however he wants it, even if it is incorrect. The opponent or a judge doesn't need to correct Storm player if it is Private information.

But the ability Storm is a single trigger and if Storm player announces it and says an incorrect number of copies on the stack, then yes, the opponent or a judge needs to intervene, after all it's not a missed trigger but a GRV.

Basically you can let your opponent count too high if he did a mistake and if he casts what he think is a total of 10 Tendrils of Agony to kill you you can tell him “Nope, it's only 9” and proceed to win the game. But if he casts it announcing a lower number than the correct one you'll also need to correct him and take the life loss.

That's only my opinion though.

Edited Àre Maturana (Aug. 6, 2018 01:53:18 PM)

Originally posted by Àre Maturana:

I believe this counter isn't part of the game (so it's not defined by “Free information consists of: The number and type of any counter that isn’t defined as status information.“ or status information ”Status information consists of: Counters a player has attached to them.”), and since it isn't an object or the caracteristic of an object, it's not derived information. By default it becomes Private information which Storm player is free to represent however he wants it, even if it is incorrect. The opponent or a judge doesn't need to correct Storm player if it is Private information.

Previous thread on the topic. To the best of my knowledge, nothing in that section of the MTR has changed in any way that would meaningfully affect the answer.

Originally posted by Scott Marshall:

'O'fficial confirmation: Emilien is correct. Other than a few specific things - number and type of counter, e.g. - that are listed in the Player Communication Policy as Free information, counting things is usually Derived.

“How many spells have you cast?” –> Derived, don't have to answer;
“Did you cast A, B, C, and D this turn?” –> Free, you have to answer (but if they forgot about E, you don't have to volunteer that info).

d:^D

Originally posted by Àre Maturana:

I believe this counter isn't part of the game (so it's not defined by “Free information consists of: The number and type of any counter that isn’t defined as status information.“ or status information ”Status information consists of: Counters a player has attached to them.”), and since it isn't an object or the caracteristic of an object, it's not derived information. By default it becomes Private information which Storm player is free to represent however he wants it, even if it is incorrect. The opponent or a judge doesn't need to correct Storm player if it is Private information.

Why should I represent the Storm count correctly at all?

Using this argument, there is always a net benefit in using the wrong number on the counter for my storm count. I could have a storm counter at 6 but represent it as 8, hoping my opponent will take it as face value and concede when I show my storm spell even thought he wouldn't have died… As it is “private information”, I am allowed to… right?

I could've lined up behind free information with the argument “The number and type of any counter that isn’t defined as status information. ”, but here I am surprised by that answer and I don't really see how it fits the definiton :

Derived information is information to which all players are entitled access, but opponents are not obliged to assist in determining and may require some skill or calculation to determine. Derived information consists of:
• The number of any kind of objects present in any game zone that are not defined as free information.
• All characteristics of objects in public zones that are not defined as free or status information.
• Game Rules, Tournament Policy, Oracle content and any other official information pertaining to the current tournament. Cards are considered to have their Oracle text printed on them.

But sure, if it is Derived information then the player has to be corrected ASAP, either by the opponent or by a judge, correct ?

@Jeremie : I was going by definition and agree that it isn't optimal. And while all kind of things that can be represented by counters are explicitly mentioned in the MTR, nothing seems to talk about the amount of spells played during a turn. I am actually happy that my answer was incorrect, I side for people playing Magic instead of trying to abuse MTR or IPG mechanics.

Based on the comments in this thread, especially trying to answer the question raised by Jeremie, I want to add my thoughts:

1. The “storm count” represented by whatever means (number on paper, using a dice) is not part of the game.

2. The storm count is derived information. It is only relevant when the spell with the ability “Storm” is cast and resolves.

I compare the situation to the “how big is this creature” issue, e.g. Bogles or Tarmogoyf. The controlling player doesn't have to and should never answer that question. If he offers that information and it is wrong he either commits a GRV-GPE or even worse is trying to cheat.

So, the Dice or whatever “means to track storm” is a player giving derived information by implied acition (I am NOT 100 % sure this is the right english term - German: konkludentes Handeln).

So the real question to be answered is: If a player offers derived information by implied action, does it have to be correct. In my opinion “yes”. If he offers false information he is committing GPE-GRV or Cheating. It is not relevant if he is obliged to give the information or not, as soon as he offers it, he is responsible for it being correct.

However this does not mirror to the opponent. He can let the active player do or count or calculate whatever he wants and correct him when the spell resolves. Who the judge will believe after this “mess” is told to him is a different question.

Originally posted by Denis Leber:

he either commits a GRV-GPE

Just a side note: it is not a GRV-GPE, it is a TE-CPV.