The "Uncirculated" 1999-W $10 Eagle is unusual in that it was struck from unfinished Proof dies. Until 2006, the only gold American Eagles produced at West Point were Proofs, so when an Uncirculated 1999-W $10 Eagle showed up in 2000, everyone was surprised. Two possibilities arose to explain the unusual appearance of these coins: 1) they were struck from Proof dies that had already been used to strike the designated number of Proof coins or 2) they were struck from dies that did not receive the final chromium-plating that Proof dies normally receive. Experts quickly dismissed the first hypothesis and settled on the second.
Determining how many were made is problematic, as no record exists to differentiate how many examples were struck from a single die pair (or die pairs, if multiple pairs were used). Anecdotally, Fred Weinberg reported that out of 1,500 coins examined, only 21 represented the Unfinished Die.
Question: Were these coins struck at West Point or Philadelphia? If Philadelphia, would they have been included in the mintage for the normal, Uncirculated 1999 $10 Eagles?
Sources and/or recommended reading:
"W Mint Mark Appears On Wrong Coin" by Paul Gilkes, COIN WORLD, May 15, 2000, pp. 1 and 8