Not every outing, of course, with this hunting approach, or any other as far as that is concerned, is going to produce older coins. By the same token, you may go back and re-hunt that same area with the same coil four months from now and pull a silver or a couple older types of coins from there. Why? Maybe you are simple hunting more diligently. Shorter coil swing! Listening more carefully! Working those mid tone hits from different angles striving to hear a high tone tic/chirp! Maybe today your coil is scrubbing the ground which could give you an extra inch of depth. Which, with a small coil can be the difference of hearing a 7 or 8" deep coin. And so on! Meticulous ground coverage and just inching ones way along are two really key factors for me. And, being willing to re-hunt certain spots several times, regardless of how many coils may have been over the same ground.
This type of hunting isn't for everybody. Not many, in fact, probably have the patience for it. That's why, i m h o, such spots will never be truly hunted out. HH jim tn