[hugh-avherald]

The fivefold repetition rule says that the game is drawn in the event of a fivefold repetition, regardless of actions by the arbiter or either player. (Indeed, regardless of whether an arbiter is present.) So if it's later discovered to have occurred in a game which White apparently won by checkmate, then the win is void. The rule also places a duty on the arbiter to intervene, but a failure on the arbiter to intervene has no bearing on the outcome.

[mtlmtlmtlmtl]

My bad, I did not know those details. I don't think I've ever heard of a case where it's happened this way in tournament play. I bet it has though.

Do you happen to know if this can be applied even several rounds later, in a swiss format? In most tournaments, even if there are score sheets, the arbiters rarely look over the game if the players agree on the result. And sometimes I don't look over my own games until a few days later if I'm disgusted enough with how I played...