> They don't need to classify an ACH as "completed" or "not completed", they only need to place a confidence interval on its completion state, which becomes easier as they process more transfers

They ignore financial regulations to the level of Uber ignoring taxi regulations. The difference between the taxi commission or whatever its name is in San Fran and US Department of Treasury is that the later relies on people with guns and can block customer's ability to do any financial transactions.

The reason why in the standard custodial scheme ACH transactions are fine ( but still are frowned upon ) is because the appreciating asset can be reclaimed from a custodian via courts.