The Tech Times article NASA Fails To Spot Whale-Sized Asteroid That Skimmed Past Earth says that Asteroid 2017 VL2 passed the Earth within about 120,000 km, or about 1/3 the distance of the Moon on November 9 (2017) but wasn't spotted until November 10 by Mauna Loa observatory in Hawaii. It is estimated to be about 16 to 32 meters in diameter.
Is this below the threshold where there is good data on NEOs that may impact Earth, or in fact is there not yet good data on that?
How safe are we? More specifically, is there in fact little data on potential NEOs in this size range (~30 meters)?
Slight irony in the timing - see the BBC's Asteroid close approach to test warning systems where the similarly sized and well documented 2012 TC4 which passed the Earth two months ago.
below: from here.