U.S. intelligence analysts have gained valuable insights into Islamic State’s planning and personnel from a vast cache of digital data and other material recovered from bombed-out offices, abandoned laptops and the cellphones of dead fighters in recently liberated areas of Iraq and Syria.

In the most dramatic gain, U.S. officials over the last two months have added thousands of names of known or suspected Islamic State operatives to an international watch list used at airports and other border crossings. The Interpol database now contains about 19,000 names.