The person who benefits from a mistake faces a different test from the person who notices one.

Spotting an error and profiting from one put you in different positions. The person who merely notices can raise it at low cost; the person who gains has to act against their own interest, and every reason to stay quiet will present itself as something else, as not my place, as too late now, as it would only cause trouble. The temptation is proportional to the benefit.

When an error goes your way, notice the speed with which justifications arrive. Then ask what you would advise a friend in the same position to do. Raising it early is nearly always cheaper than being found to have known, and the cost is mostly to pride rather than to anything real.