I believe the way PLUTO is organized is with 1) a value for when the building was first built, and 2) up to two most recent dates of building modification. The building modification data is itself worth exploring in some way, if anyone wants to give that a shot.

This map shows the 'first built' column, so it is strange that they would get the museum of natural history wrong.

See http://www.nyc.gov/html/dcp/pdf/bytes/pluto_datadictionary.p...