Regardless of the age of the port, and contrary to what some people believe, not all port wines need to be decanted.
Tawny Ports and full bodied, fruity Ports such as Fonseca BIN 27 do not require decanting, since they have been aged in cask or large wooden vats and filtered before bottling to remove any of the natural sediment there may have been in the wine. Simply open and these Port wines are ready for pouring.
Vintage Port wines, on the other hand, spend only 2 years in the vats before being bottled, unfiltered. Over time, and as Vintage Port ages, the wine's natural deposit builds up at the bottom of the bottle. This is why any Vintage Port must be decanted before serving to remove this deposit.
Fonseca Late Bottled Vintage Unfiltered and Fonseca Crusted, despite having aged in wood for a longer period, are bottled unfiltered. Even though they do not "form" as much deposit in the bottle as a Vintage Port, these Port wines must also be decanted in order to be enjoyed at their best.