If you are setting up these tests with everything on the surface, is there proof the errors occur at any depth? Also, if we are detecting at a school or park, is there proof that they have as many nails as the yard hunters who set up these tests? Not saying these tests are always meaningless, but in parks most coin losers don't dump a box of nails next to the coin.
If there is a situation the ID is wrong, should we dig everything and therefore dump all our detectors with discrimination in the garbage and use PI detectors only? Would this make us dig several dozen or more pieces of trash for each coin? And would most consider it worth it? It might make sense in a ghost town so old it hasn't seen modern trash. As for places still in use, wouldn't most quit the hobby if they got several dozen pieces of foil, pull tabs, steel and aluminum bottle caps, etc, for each coin? This hobby wasn't too popular before discrimination in 1970s.
Of course, we can all decide for ourselves if we dig all or are selecting only probable coins. Maybe it would be interesting to some if we had 2 groups of detectorists at same place at same time, with equal numbers in each group who would dig all or only probable coins. Which side would get the most valuables?
Yes, the dig all people would likely get more gold rings, and those using discrimination would likely get more coins. But not everyone has unlimited patience, so we might have to conclude people should do it whichever way is the most fun and relaxing. If the goal is to get the most dollars per hour, would it make sense to quit this hobby and get a 2nd job instead?
I realize their could be a sense of satisfaction in getting something of value out of a place that has not given up anything of value in years but I'd probably think why not drive another 10 miles?