In a nut shell;
The Charlton is a guide and the prices published are essentially a median note of the variety sold for at the time of publication. Prices are the collaboration and determined by a pricing panel made up of dealers & collectors. Each one submits their data, and this is then used to establish a price of what is happening in the current market. I believe this source to be a good indication of the true market price for that year, and the best source for educating yourself when buying or selling. Both Dealers and Collectors use the Charlton Guide as a bible.
The auctions will also have an impact on the market value, but be carful when using auctions as a reference. If a note is priced high, it will look really good if you have one, but it never sells. Also if there are two people that really want a note in an auction, they can drive the buy price sky high (fantasy price) when their ego’s get in the way. A rule of thumb I go by is 1st sale is a sale, 2nd sale is a trend, 3rd sale is a market.