I'm almost certain that Riverside Drive was never known as "Boulevard
Lafayette." I don't remember seeing reference to this in either Peter
Salwen's Upper West Side Story or Clarence True's Riverside Drive. When
the modern street opened in 1890 it was officially "Riverside avenue" and
was renamed "Riverside Drive" a few years later.
The "Boulevard"--the name for Broadway above 59th street until 1899--was
only two blocks east of Riverside. "Broadway-Lafeyette" is also the name
of a modern day subway station in downtown Manhattan. Perhaps this is the
source of confusion?
Jim Epstein