Given the fact that there was only a single reverse die which was missing the right foreleg, it should not come as a surprise that only a minority of all 1937-D Buffalo Nickels are the 3 Legged variety.
The total mintage for the issue was 17,826,000 coins, a reasonable number within the series, indicating the importance of the nickel denomination within American commerce. The exact number of these which were the 3 Legged variety is unknown, although it is generally assumed that the total number struck may have been around 20,000 examples.
As the variety was not discovered immediately and virtually all pieces quietly entered circulation, it took some time before they were noticed by the general public. However, once the variety became more widely known, values rose and the pieces were quickly pulled from circulation, especially since the variety was easy to spot and visible without magnification.
Many people found something magical or intriguing about a “three legged” buffalo on a circulating coin, a sentiment that persists to this day. In fact, many collectors decide to include this popular variety as the only variety in a set of Buffalo Nickels, leaving out other varieties such as the rare 1914/13 overdate and 1916 Doubled Die.