Key word in that sentence being "known". Trust, but verify. And when dealing with North Korea, verify several different ways.
Hard to hide those sites from even commercial satellite imagery, let alone military.
Yes indeed......
Some say there is no known way of detecting secret centrifuge facilities for enriching uranium because these can be smaller than an office building, would easily fit into an underground tunnel, consume very little electricity and release almost no thermal or chemical emissions..so makes them hard to find.
No matter how extensive verification will end up happening in the N.K. it’s going to be a long process.