When you look at the 1960's cents, the master hub was swelling on those years. Pretty much the same on all the cents on those years. In 1968, they were pushing on the rims. So the next year, they re-created a new master hub. That fixed that issue for a time:

By 1982, the same issue of the swollen hub was an issue again. But they changed it part way though the year, thus creating the large and small date cents:

But how did I determine that this happened? I used Photoshop to recreate a normal small date, and created a swelling from the centers of the coins.
What did I see?


So they didn't create a new design, they just recreated a new master hub:

This happens on all the master hubs, so we see other denominations that create a lot of coins, showing this every now and then

Note the differences in bust size, devices size and distortion of devices. When the devices get too close to the rim, they have to create a new master hub.
CoopHome : Die swelling