My experience has been plowing is a double-edged sword. It can bring goodies to the top, or bury them deeper.
The site of Fort Atkinson (1850-1857) is nothing but a worked field now. We have hunted it for about 40 years. Some 35 years ago I found what was the only coin for many years. A very nice 1839 half dime. We hunted it for many years after and found many buttons and musket balls. After a plow job just a few years ago my buddy found 1840 seated dime, and not 5 minutes later I found an 1835 capped bust half dime. Mine was basically on top of the ground. I got a signal, kicked the dirt, and saw a black disc slide across the ground.
Almost 30 years between the coin finds at the same location.