Even though the 1919-D is rarest in Gem form, the 1919-S contained less coins. Only 548,000 were produced at the San Francisco Mint in 1921, and many circulated.
As the economy struggled, few people could save half dollars in coin collections because many earned 50 cents an hour. In 2016, a mint state sample sold for $188,000.
The 1921-D Walking Liberty half dollar is also rare in mint state. The Denver Mint issue was heavily circulated, thus pristine copies are rare. With a good strike, the value rises. One 1921-D sold for $168,000 in 2018.
The mint transferred the mintmark to the reverse in 1917 because it seemed like a glitch in the coin die. Rare 1917 coins have the mark on the obverse. They're scarce in good condition. One sold for $152,750 in 2015.
The 1944 Walking Liberty 50-cent piece was minted in excess of 28 million, but it's nearly impossible to obtain one with great features and low circulation wear.
This coin sometimes lacks the detail needed to reveal Lady Liberty's gown folds, even in mint condition. One high-grade sold for $109,250 in 2010.