The following Q&A is excerpted from Clifford Mishler’s Coins: Questions & Answers:
Q: I have been told by some that the three-legged variety of the 1937-D Buffalo nickel was created when the engraver preparing the die made a mistake and omitted a leg. Others have said the variety was created when that area of the die became filled with a foreign material. Who has given me the correct explanation?
A: The first answer is certainly incorrect, and the second is likely incorrect as well, from the technical perspective. The creation of this error, which caught the fancy of the collecting public, is generally attributed to the fact that a Mint workman used a tool to salvage a damaged die, grinding the surface of the die “down to remove injuries sustained during its accidental clash with the obverse die.” In addition to the foreleg of the buffalo above the hoof having been removed, certain areas of detail are struck up weakly on genuine specimens as well. Beware that this error can be easily faked by carefully tooling off the foreleg of the buffalo on regular 1937-D strikes. Similar errors exist of other Buffalo nickels, but they are not widely collected because they did not catch the fancy of the collecting community, the 1936-D 3-1/2 legs error being one of them.
Q: Are the so-called restored date Buffalo nickels considered valuable as collectors’ items?
A: Not by serious collectors. An acid application makes the worn dates temporarily visible. The disappearance of the “restored” date after the coin has been passed off on an uninformed or novice collector can be of no possible benefit to the hobby.