How much is a 1971 one cent supposed to weigh,. Most of my cents weigh around 3.17. But this 1972 weighs 2.89.
3.1 should be the correct weight. But there have been Cents over the years that have been struck on thinner than normal Planchets. It happens the other way also where they have been struck on thicker Planchets. So there is a +/- variance in weight. It has to be even lighter than your finds for it to be recognized as a Mint error. Here is one from my collection at 2.43g - I have 4 of these in my collection also from the early 1970's