Many ATM's can actually detect that too much was given and report it as part of their communications protocol, it's called a "mis-dispense". Some used to even

Many ATM's can actually detect that too much was given and report it as part of their communications protocol, it's called a "mis-dispense". Some used to even be configured to not allow opening the door to get the money on mis-dispense, requiring someone from the bank to come out to clear it. Source: I used to work on the bank software side of this communication, on IBM AS/400's.