I'm not casting doubts on anyone here....
I merely stated that finding such deep targets are rare, and subject to some other factors in how they're recovered, and subsequently measured.
If a member of my club consistently came in claiming 16" finds on coins, however, I would be silently doubtful, but never proclaim fraud. Weird things happen in this hobby...after 31 years I've seen a lot. When I bring my personal experiences into play, along with those of my hunting buddies, I have a lot of info to back my beliefs on deep finds.
Again, anything is possible....just not probable.
A good case in point: One former member of our club (this was 20 years ago) found an old leather coin purse with Barber quarters, dimes, V nickels and Indian heads in it. It was a fantastic find! The coins were stacked within the rotting leather and thus showed little circles of untarnished metal where they were stacked. It was the first time I'd ever seen original mint luster on an Indian Head cent....bright, shiny copper and in great shape. The whole club went crazy over this rare multiple find and this guy got tons of attention and congratulatory back slaps, and rightly so. But apparently, this fellow had few other things in life that gave him such attention. The next month he turned up with another multiple find...two Barber halves and a few dimes he said were in the same hole...a yard find. Every month thereafter, for 5 months he presented multiple finds, each one more sensational than the last. Eventually, his finds weren't fussed over and were actually ignored. They didn't receive one vote for find of the month. Single Indian Head cents got more votes than his small handfuls of Barber and Seated silver. Without saying a word, or accusing in any way, the club had silently decided that his finds were just too improbable...too good to be true with such frequency. I think he finally got the message as his finds started to become more credible after that. Now, its possible that everything he found was legit...an incredible run of luck. But the improbability of it all was just too much to accept, being that before he found the original coin purse, he had typical finds with an occasional nice old coin to show for his efforts.
So while I will concede finding coins at great depths is possible (my friends and I have all had a few really deep ones) , I just don't see it as a consistent, every day occurrence for any given hunter, regardless of machine or technique, happening at different sights and under different conditions. Thank God, too, as I wouldn't have the energy to dig that deep on every signal!
Really, it doesn't matter to me how deep someone finds or says they found a coin. The only thing tangible after a target recovery is the target itself, and that's what you can literally take to the bank.
Knipper