I believe that modern slot machines used (before they mostly went coinless) a comparator much like a Ryedale. They would not accept silver coins. So even though they would spit out any silver that had been dumped into their till as payment, that coin would not have been accepted by the machine if someone attempted to put it back in. So many just likely went into someone's pocket whether they knew of silver coins or not. Not 100% sure on that, but thats what I have been told.
At one casino I used to frequent often back in the 1990's and early 2000's, there was one older gentleman that was almost always at the poker tables CRHing halves as he played. He'd buy $300, search them, cash 'em in and do it all over again - all night long. I watched him do this for years and years until the casino went coinless. I personally saw him search tens of thousands, if not hundreds of thousands of dollars. During all that time, I saw him pull 1 40%er. That particular casino used halves on their poker tables for rake purposes. I no doubt played MANY thousands of hands at that casino, and saw many many rolls of halves opened. During all that time, I saw only 1 40%er hit the table.