1974-D Penny Small Head

It's hard to tell from your images which of the two you have in each of those images, small date or large date--but at any rate, that's not really what you're reporting with your find. What you have found is a case of die polishing (small head) that began to take away parts of the design from the underside up...which shrank the apparent size of the head. This happens often on cents.

What I don't believe you are aware of is the fact that there actually are two different date sizes for 1974 cents, small date and large date. It is believed that the change took place so the metal would flow better into the dies for the proposed aluminum cent that never came to pass. At any rate, the two types exist for all mints in 1974, but the proof cents are all large date.

Furthermore, a study is still underway, but there are also two different styles of mintmarks on 1974S cents, both proof and business strike. There was a style of mintmark introduced in 1971 that was still in use in 1974, and a new style was introduced in 1974 that lasted until 1979.

Have fun!