The most straightforward criterion would probably be “things they themselves feel to be mistakes a year or two later”. That risks people just failing to own their mistakes so would only work with people I felt enough trust in to be honest with themselves. Alternatively you could have an impartial judge. (I’d rather defer to “someone reasonable making judgements” than try to define exactly what a mistake is, because the latter would cover a lot of ground and I don’t think I’d do a good job of it; also my claims don’t feel super sensitive to how mistakes are defined.)
The most straightforward criterion would probably be “things they themselves feel to be mistakes a year or two later”. That risks people just failing to own their mistakes so would only work with people I felt enough trust in to be honest with themselves. Alternatively you could have an impartial judge. (I’d rather defer to “someone reasonable making judgements” than try to define exactly what a mistake is, because the latter would cover a lot of ground and I don’t think I’d do a good job of it; also my claims don’t feel super sensitive to how mistakes are defined.)