Key Date U.S. Coins of the 20th Century

Set Description
This Set is inspired by the U.S. 20th Century Series Type Set category in the NGC Registry and consists of the key dates of those Coins. The set does not include gold, proofs, or inadvertent Irregularities.
Not all will be mint state, just the best affordable coins. Not all coins will be rare or valuable. Some will be what I consider the most significant or interesting coin for the series and I will attempt to qualify the coins in comments.

Set Goals
I have collected coins from all series' of 20th Century US Coins. I decided to downsize my collection but I could not choose a favorite series. I have decided to focus on quality over quantity and collect the Key Coins of those series. I will attempt to fill all of the slots and look for opportunities to improve on the grade of each coin I own.