Ok i know saga's lore counters are mandatory and will be done once the player is done with the draw step at the start of main phase 1.

Assumig a saga has 2 lore counter (for purpose of the example let us use time in the ice)
Player controlling time in the ice drew and proceeded with his main phase and forgot to put a lore counter to trigger the 3rd chapter.

Assuming this is under competitive.
Here are the scenarios that we have a conflict of interest.

A) player activates an ability of his planes walker and after resolving it noticed that they failed to add the lore counter.
- would a back up be done since it was caught within a reasonable time and a grv will be given to the player and failure to maintain game state to the opponent?

B) player declares his attacks and after blockers have been assigned and damage has been dealt that the player noticed they failed to add the lore counter which would cause the creatures to be return to the opponent's hand
-would you put the lore counter on the chapter and issued a missed trigger violation and rule the saga be sacrificed without triggering the 3rd chapter?
**would it be different if it was caught prior to damage dealt or blockers declared and back up would be done?

C) would it be any different in a regular setting?

Edited Allen Vincent Balean (May 7, 2018 08:42:03 AM)

In any case, it's a GRV, possibly Failure to Maintain Game State (FtMGS) for the opponent - who, after all, is responsible for making sure the Lore counters are handled correctly! - and we follow the guidelines of the IPG for any situation that might involve Backing Up.

Originally posted by IPG 1.4:

A good backup will result in a situation where the gained information makes no difference and the line of play remains the same (excepting the error, which has been fixed). This means limiting backups to situations with minimal decision trees.
-and-
Backups involving random/unknown elements should be approached with extreme caution, especially if they cause or threaten to cause a situation in which a player will end up with different cards than they would once they have correctly drawn those cards.

(A) depends on the planeswalker ability, and whether or not backing up would be worse than leaving it as is.
(B) investigate the opponent, who definitely gained an advantage (being able to block); otherwise, see (A).
(C) see (A).

Sorry, I know that's not hard & fast rules that you may have been asking for, but the many variants that exist in each of these (and all the many similar) situations demands that we follow guidelines, not “rules”.

d:^D