Perplexing: despite construction work and marketing, 550 Vanderbilt not officially "under construction"

Would you believe that Greenland Forest City Partners is marketing sales of the 550 Vanderbilt condo tower before the building is officially under construction?

Or could it be that "under construction" is some term of art that does not apply to a building site undergoing numerous construction activities?

A press release from Forest City Enterprises today regarding first quarter results citied only two Atlantic Yards/Pacific Park towers under construction:

B2 BKLYN, a 363-unit apartment community at Pacific Park Brooklyn that is being built using modular construction methods. B2 is expected to be completed in the third quarter of 2016.
535 Carlton, a 298-unit, all-affordable apartment community at Pacific Park Brooklyn. The project is part of Forest City's strategic partnership with Greenland. 535 Carlton is expected to be completed in the third quarter of 2016.

Starting in Q2?

What about the condo tower? A Form 8-K submitted today to the Securities and Exchange Commission (SEC) made it more clear:

Pacific Park Brooklyn, a 22-acre mixed-use project, is located adjacent to the state-of-the-art arena, Barclays Center. At full build-out, Pacific Park Brooklyn is expected to feature more than 6,400 units of housing, including 2,250 affordable units, approximately 250,000 square feet of retail space, and more than 8 acres of landscaped open space. Projects currently under construction include B2 BKLYN, a 50% market-rate and 50% affordable rental building with 363 residential units, and 535 Carlton, a 100% affordable rental building with 298 residential units. In Q2 2015, construction is expected to commence on a 278-unit condominium building and a 301-unit, 100% affordable rental building.

The 278-unit condo building is 550 Vanderbilt (while the affordable building is 38 Sixth Avenue).

But the Construction Updates issued every two weeks by Empire State Development after preparation by Greenland Forest City Partners regularly note construction at the site. Consider the latest, issued 4/27/15:

Or the 2/16/15 update: