You miss my point, I said "debase" not change.  Except for the WWII save copper by using steel penny, it was 95% copper from 1864 to 1982, and I can't count the two previous changes as debasing it (pure copper to a 89% copper/11% nickle alloy was surely for durability, the change 7 years later might have been related to the Civil War at the time but strikes me as the only possible previous debasement).