The prices listed are for spot-free coins. The Mints of the world have a problem with new silver coins, especially the.999 silver issues, and that problem is spotting. These modern silver coins can be found with white "milk" spots which range from a one or two light and small spots to thick, large, and numerous spots. The prices in the PCGS Price Guide are for spot-free coins. Coins with white spots will usually sell for a discount from the prices listed in the PCGS Price Guide.
For further information as to how PCGS handles spotted coins, see the following link to the in-depth discussion on modern silver coin spotting.