It is essentially a calculation based on difficulty, last block reward, and best market bid price (although the latter was manipulated from what I can best call a market price smoothing function that I don't agree with). Once the coin has matured, obviously the market price may have moved. But the best market price might not be the exchange where the coin is sent. A preferred market route might be set up, or it might send it to the big exchanges (bittrex, poloniex) in preference to the exchange with the best market price.

EDIT: Also the exchange with the best market price might not have the market depth to fill a large order at that price, so the price attained may be lower.