http://www.pcgscoinfacts.com/Coin/Detail/148715 If you look at the above, the PCGS price exceeds the apparent sales history by $700, including on the lowest listed grade, which has a PCGS value of $1100. Does PCGS simply ignore prices on varieties?
Their research of coin values requires that some purchase/auction occur AND be published where they look (Heritage? eBay? etc.) If ta new sale of a particular variety doesn't show where they're looking then they have no basis for altering their posted values. And it may even take more than one sale since reporting an anomalous result (unusually high or low) would be worse than no change.
I've found downward sale history is less likely to cause an immediate change. It could have been a poorly attended or watched auction, or it could have been not solid for the grade. Once it happens repeatedly, then they tend to act. But remember, these can be very "thin" markets. The number of bidders is often destiny.
