[akgerber]

Just because a piece of land doesn't have a building on it (even if it isn't currently legally buildable) doesn't mean its address "doesn't exist". New York City is glad to point you at the address: http://gis.nyc.gov/dcp/at/f1.jsp?submit=true&house_nbr=3...

[akgerber]

Likewise, the stretch of "E 15th St." in Brooklyn is actually named "Marlborough Rd." on the ground in the stretch where #315 is located: https://maps.google.com/maps?q=315+E+15th+St,+Flatbush+-+Dit...

It does look like the city understands the alternate name, not that that'd help you when you're out looking at street signs: http://gis.nyc.gov/dcp/at/f1.jsp?submit=true&house_nbr=3...

[barista]

Just checked and Bing gets it too!