Building Designators and the 'Address 2' Field

When should a building designator be included? Only if it appears in an official source? Should it be added in certain cases, such as when a building name is different than the feature name being captured? (e.g. a post office located in a named Federal building; a city hall located in a building called "town hall")

When should a building designator be included? Only if it appears in an official source? Should it be added in certain cases, such as when a building name is different than the feature name being captured? (e.g. a post office located in a named Federal building; a city hall located in a building called "town hall")