There are any number of ways a player can cheat and hope to get away with it with the assumption the tournament directors are not competent to catch them. The main thought
I have for such miscreants is this: your day will come, and as you seek to deny others the
pleasure of friendly competition, so it shall be denied to you.
In the tournaments in our area, it is customary that when a person’s clock drops below five minutes someone who has finished their game will begin keeping an independent record of all moves available for either/both players. Seems like a civilized thing to do and eliminates such problems, eh?
I’ve often done this for friends, but I was doing so purely so they would have the complete record of the game to go over afterward. I’m confident that my score sheet could not be used as proof of a claim. Certainly as a TD I wouldn’t accept someone making a claim based on that they had someone else keep score for them.
I guess the TD could use the helper as a witness to gather information from in certain cases, but not to use the scoresheet as evidence to support a claim that requires notation to prove. That seems to be crossing the line of using outside assistance.
A player certainly couldn’t make a claim based on a scoresheet kept by an observer. But the observer could provide testimony in the case of a claim made on the basis of a falsified scoresheet. And that fact would probably deter the falsified claim from ever being made.