When I was a starving college student, working two jobs to survive, I had a checking account at a small local bank. This was over 40 years ago when my rent was $38. a month.
I received my monthly statement by mail and it showed a deposit of over $700. which I definitely did not make. (That would be worth thousands in today's money). I was too busy to go to the bank in person and twice when I called, I was put on a long hold. I figured they would catch the error anyhow.
But month after month, the statements showed that the money was still there. My best friend dared me to go in person and "just see" if I would be able to withdraw it. I had about $50. of my own money in in the account so I asked the teller if I could withdraw $60.. I was surprised when she said that there was no limit on the amount I could withdraw, I could take everything out but that would result in the closing of the account. Well, I walked out with nothing, and owed my friend $5.00 because she bet that I could take it, and I was sure I couldn't (or might be arrested if I tried).
Subsequently I was tempted but I was really too honest to take any of the money. But I left it there "just in case something catastrophic happened" and I really, really needed the money. I kept expecting the bank to find the error.
Two years later I wanted to get this off my conscience (and out of the reach of temptation) but I felt it was "too late" to report the error. And maybe I violated some law by not doing it when it happened. So I just withdrew my own part of the money and never did any further business there. When the statements kept coming, I finally took one of them and wrote: "moved, left no forwarding address" and dropped it in a street corner mailbox.
Many years later, I saw my name on the state's list of unclaimed funds. Sure enough, the bank's name was listed with $700. due to me. (It was a non interest account). I eventually claimed the money and donated it to charity.
What a long way the banks have come from the way they operated in those days.