Why is this coin NOT in the NGC price guide?

In 2000, the Mint issued the "United States Millennium Coinage and Currency Set" which included a 2000 Silver Eagle bullion coin minted at West Point (but without a "W" mintmark), a 2000 Denver-minted Sacagawea Dollar with a burnished finish, and an uncirculated 1999 series one-dollar bill with a serial number beginning with the numbers "2000". The sets sold out at the issue limit of 75,000 units.

Here's the real question why is this coin listed as part of the Complete Silver Eagle Set but, NOT on the NGC price guide? The 2008 error and 2011 S are both limited coins and are listed but not the 2000 Millennium? Any one have the real answer?