[Nichlemn]

Surely giving a reward is +EV for Party? As it making it somewhat proportional (though obviously you couldn't give millions). This is because in the future, anyone else who accidentally got transferred $40 million, knowing they wouldn't get a cent of reward for it, has little incentive not to screw around with it and maybe try to get some out for themselves. If Party thinks the average damage the person not reporting it could cause is even 0.1% of the total amount (assuming that they could catch people trying to withdraw or chip dump a large proportion of the time), surely returning half of that expected loss, $20,000, to the honest person is reasonable.

Of course, maybe they're banking that no accidental transfers of any scale could ever occur again.

So maybe if such a thing happens to you, you could punish Party for their stinginess.