Since late January, about two weeks I reckon so far. There's some sort of spoopy shit going down with these flights and the aborted flight that returned to San Juan yesterday only aded to the intrigue. These flights are on the down-low and well away from the "Ermahgerd! DERMSDERR!" flights like the Nighthawks and Mercurys.
Maybe it's only us Planefags that were intended to spot them.