No late claims after the result of a match has been officially announced are allowed in match play rules except in cases where a player knowingly gave wrong information.
It’s a matter for the committee in charge of an event to decide when officially announced comes into play, usually when recorded on the official scoreboard.
I found it interesting that this issue came into play during the opening session of the Walker Cup at Royal Aberdeen.
It seems that Jack Senior of Great Britain/Ireland violated a rule of the competition by having his brother Joe Senior, a professional, caddy for him when he and Andy Sullivan beat the U.S. duo of Kelly Kraft and Russell Henley, 2&1.
Unfortunately for the Americans, this wasn’t discovered until the results had been officially announced.
“We were alerted to the fact that Jack Senior’s caddie may be a professional golfer after the match had finished,” explained R&A chief executive Peter Dawson. “We verified with Jack that was in fact the case. The breach of that condition was discovered after the match had finished. Had it been discovered during the match, an adjustment to the state of the match would have had to have been made and the caddie would have had to have been changed mid-round. But because it wasn’t discovered until after the result had been officially declared, the rules of golf say that the result should stand, and the result does stand and it remains 3-1 to Great Britain & Ireland.”
Of course, it would have been 2-2 otherwise and instead of losing the competition for the first time since 2003, 14-12, the Walker Cup could have ended in a 13-13 tie with the Americans keeping the cup.
Taking a closer look, it’s my opinion that maybe a case could be made that ignorance of the rules of the competition could be called giving wrong information. Evidently, no one from the USGA thought so, however.